Alexander Glazer

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Alexander Glazer was a professor of the Graduate School in the Department of Molecular and Cell Biology at the University of California, Berkeley. He had a passion for protein chemistry and structure function relationships. [1] He also had a longstanding interest in light-harvesting complexes in cyanobacteria and red algae called phycobilisomes. [2] He had also spent more than 10 years working on the human genome project where he has investigated methods for DNA detection and sequencing which most notably includes the development of fluorescent reagents involved in cell labeling. [3] Most recently, he had focused his studies on issues in environmental sciences. [3] He died on July 18, 2021, in Orinda, California

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Early life

Glazer was born in Lodz, Poland in 1935 and then moved to Australia where he earned his bachelor's and master's degrees from the University of Sydney in 1957 and 1958, respectively. His master's thesis at the University of Sydney was based on the physiochemical studies of proteins. At the University of Sydney, Glazer saw a lecture by Emil Smith on the proteolytic enzyme papain. This lecture was so inspiring for Glazer that after it, he went to the University of Utah to continue studying with Smith. He earned his Ph.D. from the University of Utah in 1960. [1]

Early career

After graduating from the University of Utah, Glazer relocated to Israel, where he completed a postdoctoral fellowship in the Department of Biophysics at the Weizmann Institute of Science. He resumed his postdoctoral work at the MRC Laboratory of Molecular Biology in Cambridge, where he researched the labeling of proteins with radioactive isotope in order to determine amino acid sequences. In 1964, he became part of the faculty of the Department of Biological Chemistry at the University of California Los Angeles School of Medicine. [1] Glazer is now a professor of the Graduate School Division of Biochemistry, Biophysics and Structural Biology. [4]

Research on cyanobacteria and red algae

The light reactions in photosynthesis start with an antenna complex absorbing a photon. This excitation energy is transferred from one chromophore to another and ends at a pair of chlorophyll molecules in a transmembrane reaction center complex. Each transmembrane reaction center complex is associated with an antenna complex that has hundreds of light-harvesting pigment molecules. [5] In fact, a common feature of all photosynthetic machinery in bacteria, algae and plants is the existence of many antenna complexes that can absorb the light and transfer it to a transmembrane reaction center complex. [6] The light-harvesting pigment molecules are made of proteins that are covalently attached to open chain tetrapyrrole prosthetic groups called bilins that can absorb light. [6] These antenna assemblies within cyanobacteria and red algae are called phycobilisomes. These phycobilisomes are of particular interest to scientists because they are the biggest light-harvesting complexes that can be isolated and studied without disruption to the cell. [2] They are able to be isolated from the cell easily because they are located on the peripheral membrane and can be easily separated from the photosynthetic lamellae by mild detergent. [6]

In one study, Glazer and his colleague Suen Fang analyzed the chromophore content of a blue-green algae called phycocyanin and allophycocyanin that was derived from Synechococcus sp., which is a unicellular cyanobacterium. [1] They found that the phycocyanin carried three phycocyanobilin chromophores, two of which were bound to a beta subunit and one of which was bound to an alpha subunit. Furthermore, in experiments with blue-green algae other than those derived from Synechococcus sp. it was concluded that this discovered chromophore distribution is maintained among most cyanophytan phycobiliproteins. [7] This study determined the distribution of the chromophores in the blue-green algae phycocyanin.

Glazer also investigated the structural and molecular organization of the photosynthetic accessory pigments in Cyanobacteria, which are the blue-green algae, and in Rhodophyta, which are the red algae. Both of these algae have high levels of photosynthetic accessory pigments, called phycobiliproteins, which collect light energy around 525 nm. The phycobiliproteins are easy to study because they are soluble in aqueous solution, can be easily isolated and crystallize readily. Thus, this allows them to be examined easily through X-ray diffraction and electron microscopy. In vivo, these phycobiliproteins were able to be organized onto the surface of photosynthetic lamellae to investigate the specific pathway of energy transfer. The following pathway was discovered: Phycoerythrin → Phycocyanin → (λmax ~ 560 nm) (λmax ~ 620 nm) Allophycocyanin → Allophycocyanin B → (λmax 650 nm)(λmax 671 nm) Chlorophyll a (λmax 680 nm). [8] Overall, his work showed that the phycobilisomes have a specific directional pathway for energy transfer towards the reaction center regardless of where this light harvesting complex is located. [2]

Glazer also examined the process of making a fluorescent holophycobiliprotein subunit from a cyanobacterium in Escherichia coli. [9] This was significant because it showed that it was possible to produce these proteins in situ where they could be used as fluorescent protein probes in living cells. Glazer also examined the physical and spectroscopic properties of phycobiliproteins. [10] Due to their brightly colored nature, he noted how they could be used in flow cytometry and in the detection of reactive oxygen species.

Research on environmental science

Most recently, Glazer has shifted his attention to focus on diverse issues in environmental science, such as the impact of anthropogenic fixed nitrogen, the lack of and contamination of freshwater sources, and the impacts of natural gas and oil production. [4]

Anthropogenic fixed nitrogen has originated from human activity. Glazer discussed in a published paper from 2010 that throughout the past century, new agriculture practices to meet the growing food demand have negatively impacted the nitrogen cycle. This has caused excessive richness in nutrients due to runoff but also an increase in animal death due to a lack of oxygen. He also noted that there has been a drastic increase in the greenhouse gas, nitrous oxide. Glazer notes that the damage caused by human activities to the nitrogen cycle could last for decades if large scale interventions are not implemented soon. [11]

Glazer also investigated the depletion and contamination of freshwater resources in detail. Overly dry land and semi dry land are home to over 38% of the world's population and has become a limiting resource here. Withdrawal of groundwater, which is freshwater in the soil that is stored in pores between rocks and soil particles, has severely impacted the groundwater dependent ecosystems. Glazer has focused on the challenges involved with replacing groundwater and analyzes if the costs of these groundwater withdrawals are being recognized. [12]

Glazer has also analyzed the importance of natural reserves. These areas help protect wilderness and biodiversity, are important for scientific research, maintain traditions and can be used for educational purposes. Over 12.5% of earth's surface is covered in natural reserves but there are currently many threats to them that are leading to an uncertain future. [13]

Furthermore, Glazer analyzed the conserved amino acid sequence features in MoFe, VFe, and FeFe alpha subunits to determine if there is an evolutionary trend flowing from one type of nitrogenase to another. [14] Finally, Glazer explored the occurrence of lateral gene transfer by using nitrogen fixation genes. This investigation sought to determine the occurrence of lateral gene transfer in the context of prokaryotic nitrogen fixation. [15]

Memberships

Awards and honors

Related Research Articles

<span class="mw-page-title-main">Cytochrome</span> Redox-active proteins containing a heme with a Fe atom as a cofactor

Cytochromes are redox-active proteins containing a heme, with a central iron (Fe) atom at its core, as a cofactor. They are involved in electron transport chain and redox catalysis. They are classified according to the type of heme and its mode of binding. Four varieties are recognized by the International Union of Biochemistry and Molecular Biology (IUBMB), cytochromes a, cytochromes b, cytochromes c and cytochrome d.

Phycobilins are light-capturing bilins found in cyanobacteria and in the chloroplasts of red algae, glaucophytes and some cryptomonads. Most of their molecules consist of a chromophore which makes them coloured. They are unique among the photosynthetic pigments in that they are bonded to certain water-soluble proteins, known as phycobiliproteins. Phycobiliproteins then pass the light energy to chlorophylls for photosynthesis.

Phycoerythrin (PE) is a red protein-pigment complex from the light-harvesting phycobiliprotein family, present in cyanobacteria, red algae and cryptophytes, accessory to the main chlorophyll pigments responsible for photosynthesis.The red pigment is due to the prosthetic group, phycoerythrobilin, which gives phycoerythrin its red color.

<span class="mw-page-title-main">Photosystem</span> Structural units of protein involved in photosynthesis

Photosystems are functional and structural units of protein complexes involved in photosynthesis. Together they carry out the primary photochemistry of photosynthesis: the absorption of light and the transfer of energy and electrons. Photosystems are found in the thylakoid membranes of plants, algae, and cyanobacteria. These membranes are located inside the chloroplasts of plants and algae, and in the cytoplasmic membrane of photosynthetic bacteria. There are two kinds of photosystems: PSI and PSII.

Accessory pigments are light-absorbing compounds, found in photosynthetic organisms, that work in conjunction with chlorophyll a. They include other forms of this pigment, such as chlorophyll b in green algal and vascular ("higher") plant antennae, while other algae may contain chlorophyll c or d. In addition, there are many non-chlorophyll accessory pigments, such as carotenoids or phycobiliproteins, which also absorb light and transfer that light energy to photosystem chlorophyll. Some of these accessory pigments, in particular the carotenoids, also serve to absorb and dissipate excess light energy, or work as antioxidants. The large, physically associated group of chlorophylls and other accessory pigments is sometimes referred to as a pigment bed.

<span class="mw-page-title-main">Phycocyanin</span> Protein complexes in algae

Phycocyanin is a pigment-protein complex from the light-harvesting phycobiliprotein family, along with allophycocyanin and phycoerythrin. It is an accessory pigment to chlorophyll. All phycobiliproteins are water-soluble, so they cannot exist within the membrane like carotenoids can. Instead, phycobiliproteins aggregate to form clusters that adhere to the membrane called phycobilisomes. Phycocyanin is a characteristic light blue color, absorbing orange and red light, particularly near 620 nm, and emits fluorescence at about 650 nm. Allophycocyanin absorbs and emits at longer wavelengths than phycocyanin C or phycocyanin R. Phycocyanins are found in cyanobacteria. Phycobiliproteins have fluorescent properties that are used in immunoassay kits. Phycocyanin is from the Greek phyco meaning “algae” and cyanin is from the English word “cyan", which conventionally means a shade of blue-green and is derived from the Greek “kyanos" which means a somewhat different color: "dark blue". The product phycocyanin, produced by Aphanizomenon flos-aquae and Spirulina, is for example used in the food and beverage industry as the natural coloring agent 'Lina Blue' or 'EXBERRY Shade Blue' and is found in sweets and ice cream. In addition, fluorescence detection of phycocyanin pigments in water samples is a useful method to monitor cyanobacteria biomass.

<span class="mw-page-title-main">Phycobilisome</span> Light-energy harvesting structure in cyanobacteria and red algae

Phycobilisomes are light harvesting antennae of photosystem II in cyanobacteria, red algae and glaucophytes. It was lost in the plastids of green algae / plants (chloroplasts).

<span class="mw-page-title-main">Allophycocyanin</span>

Allophycocyanin is a protein from the light-harvesting phycobiliprotein family, along with phycocyanin, phycoerythrin and phycoerythrocyanin. It is an accessory pigment to chlorophyll. All phycobiliproteins are water-soluble and therefore cannot exist within the membrane like carotenoids, but aggregate, forming clusters that adhere to the membrane called phycobilisomes. Allophycocyanin absorbs and emits red light, and is readily found in Cyanobacteria, and red algae. Phycobilin pigments have fluorescent properties that are used in immunoassay kits. In flow cytometry, it is often abbreviated APC. To be effectively used in applications such as FACS, High-Throughput Screening (HTS) and microscopy, APC needs to be chemically cross-linked.

<span class="mw-page-title-main">Phycobiliprotein</span>

Phycobiliproteins are water-soluble proteins present in cyanobacteria and certain algae. They capture light energy, which is then passed on to chlorophylls during photosynthesis. Phycobiliproteins are formed of a complex between proteins and covalently bound phycobilins that act as chromophores. They are most important constituents of the phycobilisomes.

<span class="mw-page-title-main">Phycoerythrobilin</span> Chemical compound

Phycoerythrobilin is a red phycobilin, i.e. an open tetrapyrrole chromophore found in cyanobacteria and in the chloroplasts of red algae, glaucophytes and some cryptomonads. Phycoerythrobilin is present in the phycobiliprotein phycoerythrin, of which it is the terminal acceptor of energy. The amount of phycoerythrobilin in phycoerythrins varies a lot, depending on the considered organism. In some Rhodophytes and oceanic cyanobacteria, phycoerythrobilin is also present in the phycocyanin, then termed R-phycocyanin. Like all phycobilins, phycoerythrobilin is covalently linked to these phycobiliproteins by a thioether bond.

<span class="mw-page-title-main">Photosynthetic reaction centre</span> Molecular unit responsible for absorbing light in photosynthesis

A photosynthetic reaction center is a complex of several proteins, pigments and other co-factors that together execute the primary energy conversion reactions of photosynthesis. Molecular excitations, either originating directly from sunlight or transferred as excitation energy via light-harvesting antenna systems, give rise to electron transfer reactions along the path of a series of protein-bound co-factors. These co-factors are light-absorbing molecules (also named chromophores or pigments) such as chlorophyll and pheophytin, as well as quinones. The energy of the photon is used to excite an electron of a pigment. The free energy created is then used, via a chain of nearby electron acceptors, for a transfer of hydrogen atoms (as protons and electrons) from H2O or hydrogen sulfide towards carbon dioxide, eventually producing glucose. These electron transfer steps ultimately result in the conversion of the energy of photons to chemical energy.

A light-harvesting complex consists of a number of chromophores which are complex subunit proteins that may be part of a larger super complex of a photosystem, the functional unit in photosynthesis. It is used by plants and photosynthetic bacteria to collect more of the incoming light than would be captured by the photosynthetic reaction center alone. The light which is captured by the chromophores is capable of exciting molecules from their ground state to a higher energy state, known as the excited state. This excited state does not last very long and is known to be short-lived.

<span class="mw-page-title-main">Biological pigment</span> Substances produced by living organisms

Biological pigments, also known simply as pigments or biochromes, are substances produced by living organisms that have a color resulting from selective color absorption. Biological pigments include plant pigments and flower pigments. Many biological structures, such as skin, eyes, feathers, fur and hair contain pigments such as melanin in specialized cells called chromatophores. In some species, pigments accrue over very long periods during an individual's lifespan.

Phycoerythrocyanin is a kind of phycobiliprotein, magenta chromoprotein involved in photosynthesis of some Cyanobacteria. This chromoprotein consists of alpha- and beta-subunits, generally aggregated as hexamer. Alpha-phycoerythrocyanin contains a phycoviolobilin, a violet bilin, that covalently attached at Cys-84, and beta-phycoerythrocyanin contains two phycocyanobilins, a blue bilin, that covalently attached at Cys-84 and -155, respectively. Phycoerythrocyanin is similar to phycocyanin, an important component of the light-harvesting complex (phycobilisome) of cyanobacteria and red algae.

<span class="mw-page-title-main">Phycourobilin</span> Chemical compound

Phycourobilin is an orange tetrapyrrole involved in photosynthesis in cyanobacteria and red algae. This chromophore is bound to the phycobiliprotein phycoerythrin, the distal component of the light-harvesting system of cyanobacteria and red algae (phycobilisome).

<span class="mw-page-title-main">Phycocyanobilin</span> Chemical compound

Phycocyanobilin is a blue phycobilin, i.e., a tetrapyrrole chromophore found in cyanobacteria and in the chloroplasts of red algae, glaucophytes, and some cryptomonads. Phycocyanobilin is present only in the phycobiliproteins allophycocyanin and phycocyanin, of which it is the terminal acceptor of energy. It is covalently linked to these phycobiliproteins by a thioether bond.

<span class="mw-page-title-main">Photosynthetic reaction centre protein family</span>

Photosynthetic reaction centre proteins are main protein components of photosynthetic reaction centres (RCs) of bacteria and plants. They are transmembrane proteins embedded in the chloroplast thylakoid or bacterial cell membrane.

<span class="mw-page-title-main">Ycf9 protein domain</span> Plastid protein involved in photosynthesis

In molecular biology, the PsbZ (Ycf9) is a protein domain, which is low in molecular weight. It is a transmembrane protein and therefore is located in the thylakoid membrane of chloroplasts in cyanobacteria and plants. More specifically, it is located in Photosystem II (PSII) and in the light-harvesting complex II (LHCII). Ycf9 acts as a structural linker, that stabilises the PSII-LHCII supercomplexes. Moreover, the supercomplex fails to form in PsbZ-deficient mutants, providing further evidence to suggest Ycf9's role as a structural linker. This may be caused by a marked decrease in two LHCII antenna proteins, CP26 and CP29, found in PsbZ-deficient mutants, which result in structural changes, as well as functional modifications in PSII.

In photosynthesis, state transitions are rearrangements of the photosynthetic apparatus which occur on short time-scales. The effect is prominent in cyanobacteria, whereby the phycobilisome light-harvesting antenna complexes alter their preference for transfer of excitation energy between the two reaction centers, PS I and PS II. This shift helps to minimize photodamage caused by reactive oxygen species (ROS) under stressful conditions such as high light, but may also be used to offset imbalances between the rates of generating reductant and ATP.

<span class="mw-page-title-main">Biliprotein</span>

Biliproteins are pigment protein compounds that are located in photosynthesising organisms such as algae and certain insects. They refer to any protein that contains a bilin chromophore. In plants and algae, the main function of biliproteins is to make the process of light accumulation required for photosynthesis more efficient; while in insects they play a role in growth and development. Some of their properties: including light-receptivity, light-harvesting and fluorescence have made them suitable for applications in bioimaging and as indicators; while other properties such as anti-oxidation, anti-aging and anti-inflammation in phycobiliproteins have given them potential for use in medicine, cosmetics and food technology. While research on biliproteins dates back as far as 1950, it was hindered due to issues regarding biliprotein structure, lack of methods available for isolating individual biliprotein components, as well as limited information on lyase reactions . Research on biliproteins has also been primarily focused on phycobiliproteins; but advances in technology and methodology, along with the discovery of different types of lyases, has renewed interest in biliprotein research, allowing new opportunities for investigating biliprotein processes such as assembly/disassembly and protein folding.

References

  1. 1 2 3 4 5 6 7 8 9 Kresge, Nicole; Simoni, Robert D.; Hill, Robert L. (2009-09-04). "Phycobilisome Architecture: the Work of Alexander N. Glazer". Journal of Biological Chemistry. 284 (36): e12–e14. doi: 10.1016/S0021-9258(19)54831-1 . ISSN   0021-9258. PMC   2781545 . PMID   19891052.
  2. 1 2 3 "Alexander Glazer". www.nasonline.org. Retrieved 2021-04-13.
  3. 1 2 3 4 "Alexander N. Glazer". American Academy of Arts & Sciences. Retrieved 2021-04-13.
  4. 1 2 "Faculty Research Page". Department of Molecular & Cell Biology. Retrieved 2021-04-13.
  5. ↑ Glazer, A. N. (1989-01-05). "Light guides. Directional energy transfer in a photosynthetic antenna". The Journal of Biological Chemistry. 264 (1): 1–4. doi: 10.1016/S0021-9258(17)31212-7 . ISSN   0021-9258. PMID   2491842.
  6. 1 2 3 Glazer, A N (June 1985). "Light Harvesting by Phycobilisomes". Annual Review of Biophysics and Biophysical Chemistry. 14 (1): 47–77. doi:10.1146/annurev.bb.14.060185.000403. ISSN   0883-9182. PMID   3924069.
  7. ↑ Glazer, Alexander N.; Fang, Suen (1973-01-25). "Chromophore Content of Blue-Green Algal Phycobiliproteins". Journal of Biological Chemistry. 248 (2): 659–662. doi: 10.1016/S0021-9258(19)44424-4 . ISSN   0021-9258. PMID   4630849.
  8. ↑ Glazer, Alexander N. (1977-12-01). "Structure and molecular organization of the photosynthetic accessory pigments of cyanobacteria and red algae". Molecular and Cellular Biochemistry. 18 (2): 125–140. doi:10.1007/BF00280278. ISSN   1573-4919. PMID   415227. S2CID   5851975.
  9. ↑ Tooley, Aaron J.; Cai, Yuping A.; Glazer, Alexander N. (2001-09-11). "Biosynthesis of a fluorescent cyanobacterial C-phycocyanin holo-α subunit in a heterologous host". Proceedings of the National Academy of Sciences. 98 (19): 10560–10565. Bibcode:2001PNAS...9810560T. doi: 10.1073/pnas.181340998 . ISSN   0027-8424. PMC   58505 . PMID   11553806.
  10. ↑ Glazer, Alexander N. (1994-04-01). "Phycobiliproteins — a family of valuable, widely used fluorophores". Journal of Applied Phycology. 6 (2): 105–112. doi:10.1007/BF02186064. ISSN   1573-5176. S2CID   27232037.
  11. ↑ Canfield, Donald E.; Glazer, Alexander N.; Falkowski, Paul G. (2010-10-08). "The Evolution and Future of Earth's Nitrogen Cycle". Science. 330 (6001): 192–196. Bibcode:2010Sci...330..192C. doi:10.1126/science.1186120. ISSN   0036-8075. PMID   20929768. S2CID   15189043.
  12. ↑ Glazer, Alexander N.; Likens, Gene E. (November 2012). "The Water Table: The Shifting Foundation of Life on Land". Ambio. 41 (7): 657–669. doi:10.1007/s13280-012-0328-8. ISSN   0044-7447. PMC   3472013 . PMID   22773380.
  13. ↑ Glazer, Alexander N. (2013-01-01). "Natural Reserves and Preserves". Encyclopedia of Biodiversity. pp. 442–450. doi:10.1016/B978-0-12-384719-5.00286-0. ISBN   9780123847201.
  14. ↑ Glazer, Alexander N.; Kechris, Katerina J. (2009-07-03). "Conserved amino acid sequence features in the alpha subunits of MoFe, VFe, and FeFe nitrogenases". PLOS ONE. 4 (7): e6136. Bibcode:2009PLoSO...4.6136G. doi: 10.1371/journal.pone.0006136 . ISSN   1932-6203. PMC   2700964 . PMID   19578539.
  15. ↑ Kechris, Katherina J.; Lin, Jason C.; Bickel, Peter J.; Glazer, Alexander N. (2006-06-20). "Quantitative exploration of the occurrence of lateral gene transfer by using nitrogen fixation genes as a case study". Proceedings of the National Academy of Sciences of the United States of America. 103 (25): 9584–9589. Bibcode:2006PNAS..103.9584K. doi: 10.1073/pnas.0603534103 . ISSN   0027-8424. PMC   1480450 . PMID   16769896.
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