The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum (RER), and smooth endoplasmic reticulum (SER). The endoplasmic reticulum is found in most eukaryotic cells and forms an interconnected network of flattened, membrane-enclosed sacs known as cisternae, and tubular structures in the SER. The membranes of the ER are continuous with the outer nuclear membrane. The endoplasmic reticulum is not found in red blood cells, or spermatozoa.
Protein targeting or protein sorting is the biological mechanism by which proteins are transported to their appropriate destinations within or outside the cell. Proteins can be targeted to the inner space of an organelle, different intracellular membranes, the plasma membrane, or to the exterior of the cell via secretion. Information contained in the protein itself directs this delivery process. Correct sorting is crucial for the cell; errors or dysfunction in sorting have been linked to multiple diseases.
Ribosomes are macromolecular machines, found within all cells, that perform biological protein synthesis. Ribosomal RNA is found in the ribosomal nucleus where this synthesis happens. Ribosomes link amino acids together in the order specified by the codons of messenger RNA molecules to form polypeptide chains. Ribosomes consist of two major components: the small and large ribosomal subunits. Each subunit consists of one or more ribosomal RNA molecules and many ribosomal proteins. The ribosomes and associated molecules are also known as the translational apparatus.
A signal peptide is a short peptide present at the N-terminus of most newly synthesized proteins that are destined toward the secretory pathway. These proteins include those that reside either inside certain organelles, secreted from the cell, or inserted into most cellular membranes. Although most type I membrane-bound proteins have signal peptides, most type II and multi-spanning membrane-bound proteins are targeted to the secretory pathway by their first transmembrane domain, which biochemically resembles a signal sequence except that it is not cleaved. They are a kind of target peptide.
The translocon is a complex of proteins associated with the translocation of polypeptides across membranes. In eukaryotes the term translocon most commonly refers to the complex that transports nascent polypeptides with a targeting signal sequence into the interior space of the endoplasmic reticulum (ER) from the cytosol. This translocation process requires the protein to cross a hydrophobic lipid bilayer. The same complex is also used to integrate nascent proteins into the membrane itself. In prokaryotes, a similar protein complex transports polypeptides across the (inner) plasma membrane or integrates membrane proteins. In either case, the protein complex are formed from Sec proteins, with the heterotrimeric Sec61 being the channel. In prokaryotes, the homologous channel complex is known as SecYEG.
Sec61, termed SecYEG in prokaryotes, is a membrane protein complex found in all domains of life. As the core component of the translocon, it transports proteins to the endoplasmic reticulum in eukaryotes and out of the cell in prokaryotes. It is a doughnut-shaped pore through the membrane with 3 different subunits (heterotrimeric), SecY (α), SecE (γ), and SecG (β). It has a region called the plug that blocks transport into or out of the ER. This plug is displaced when the hydrophobic region of a nascent polypeptide interacts with another region of Sec61 called the seam, allowing translocation of the polypeptide into the ER lumen.
Venkatraman "Venki" Ramakrishnan is a British-American structural biologist. He shared the 2009 Nobel Prize in Chemistry with Thomas A. Steitz and Ada Yonath for research on the structure and function of ribosomes.
The prokaryotic small ribosomal subunit, or 30S subunit, is the smaller subunit of the 70S ribosome found in prokaryotes. It is a complex of the 16S ribosomal RNA (rRNA) and 19 proteins. This complex is implicated in the binding of transfer RNA to messenger RNA (mRNA). The small subunit is responsible for the binding and the reading of the mRNA during translation. The small subunit, both the rRNA and its proteins, complexes with the large 50S subunit to form the 70S prokaryotic ribosome in prokaryotic cells. This 70S ribosome is then used to translate mRNA into proteins.
Peter S. Kim is an American scientist. He was president of Merck Research Laboratories (MRL) 2003–2013 and is currently Virginia & D.K. Ludwig Professor of Biochemistry at Stanford University, Institute Scholar at Stanford ChEM-H, and Lead Investigator of the Infectious Disease Initiative at the Chan Zuckerberg Biohub.
Tom Abraham Rapoport is a German-American cell biologist who studies protein transport in cells. Currently, he is a professor at Harvard Medical School and a Howard Hughes Medical Institute investigator. Born in Cincinnati, Ohio, he grew up in East Germany. In 1995 he accepted an offer to become a professor at Harvard Medical School. In 1997 he became an investigator of the Howard Hughes Medical Institute. He is a member of the American and German National Academies of Science.
The term macromolecular assembly (MA) refers to massive chemical structures such as viruses and non-biologic nanoparticles, cellular organelles and membranes and ribosomes, etc. that are complex mixtures of polypeptide, polynucleotide, polysaccharide or other polymeric macromolecules. They are generally of more than one of these types, and the mixtures are defined spatially, and with regard to their underlying chemical composition and structure. Macromolecules are found in living and nonliving things, and are composed of many hundreds or thousands of atoms held together by covalent bonds; they are often characterized by repeating units. Assemblies of these can likewise be biologic or non-biologic, though the MA term is more commonly applied in biology, and the term supramolecular assembly is more often applied in non-biologic contexts. MAs of macromolecules are held in their defined forms by non-covalent intermolecular interactions, and can be in either non-repeating structures, or in repeating linear, circular, spiral, or other patterns. The process by which MAs are formed has been termed molecular self-assembly, a term especially applied in non-biologic contexts. A wide variety of physical/biophysical, chemical/biochemical, and computational methods exist for the study of MA; given the scale of MAs, efforts to elaborate their composition and structure and discern mechanisms underlying their functions are at the forefront of modern structure science.
A target peptide is a short peptide chain that directs the transport of a protein to a specific region in the cell, including the nucleus, mitochondria, endoplasmic reticulum (ER), chloroplast, apoplast, peroxisome and plasma membrane. Some target peptides are cleaved from the protein by signal peptidases after the proteins are transported.
Stephen C. Harrison is professor of biological chemistry and molecular pharmacology, professor of pediatrics, and director of the Center for Molecular and Cellular Dynamics of Harvard Medical School, head of the Laboratory of Molecular Medicine at Boston Children's Hospital, and investigator of the Howard Hughes Medical Institute.
Lalita Ramakrishnan is an Indian-born American microbiologist who is known for her contributions to the understanding of the biological mechanism of tuberculosis. As of 2019 she serves as a professor of Immunology and Infectious Diseases at the University of Cambridge, where she is also a Wellcome Trust Principal Research Fellow and a practicing physician. Her research is conducted at the MRC Laboratory of Molecular Biology, where she serves as the Head of the Molecular Immunity Unit of the Department of Medicine embedded at the MRC LMB. Working with Stanley Falkow at Stanford, she developed the strategy of using Mycobacterium marinum infection as a model for tuberculosis. Her work has appeared in a number of journals, including Science, Nature, and Cell. In 2018 and 2019 Ramakrishnan coauthored two influential papers in the British Medical Journal (BMJ) arguing that the widely accepted estimates of the prevalence of latent tuberculosis—estimates used as a basis for allocation of research funds—are far too high. She is married to Mark Troll, a physical chemist.
Raymond Joseph Deshaies is an American biochemist and cell biologist. He is senior vice president of global research at Amgen and a visiting associate at the California Institute of Technology (Caltech). Prior to that, he was a professor of biology at Caltech and an investigator of the Howard Hughes Medical Institute. He is also the co-founder of the biotechnology companies Proteolix and Cleave Biosciences. His research focuses on mechanisms and regulation of protein homeostasis in eukaryotic cells, with a particular focus on how proteins are conjugated with ubiquitin and degraded by the proteasome.
Tracy Palmer is a professor of microbiology in the Biosciences Institute at Newcastle University in Tyne & Wear, England. She is known for her work on the twin-arginine translocation (Tat) pathway.
Andrew P. Carter is a British structural biologist who works at the Medical Research Council (MRC) Laboratory of Molecular Biology (LMB) in Cambridge, UK. He is known for his work on the microtubule motor dynein.
Bacterial secretion systems are protein complexes present on the cell membranes of bacteria for secretion of substances. Specifically, they are the cellular devices used by pathogenic bacteria to secrete their virulence factors to invade the host cells. They can be classified into different types based on their specific structure, composition and activity. Generally, proteins can be secreted through two different processes. One process is a one-step mechanism in which proteins from the cytoplasm of bacteria are transported and delivered directly through the cell membrane into the host cell. Another involves a two-step activity in which the proteins are first transported out of the inner cell membrane, then deposited in the periplasm, and finally through the outer cell membrane into the host cell.
Sean Whelan is a British-American virologist. He is known for identifying the cellular protein used as a receptor by Ebola virus, for defining the entry pathway that rabies virus uses to enter neurons, and for identifying the ribosome as a possible target for antiviral drugs. In July 2019, he was announced as the new Chair of the Department of Molecular Microbiology at Washington University School of Medicine in St Louis, Missouri. In February 2020, Whelan was recognized as the LGBTQ+ Scientist of the Year 2020 by the National Organization of Gay and Lesbian Scientists and Technical Professionals.
Tanja Kortemme is a bioengineering professor at University of California, San Francisco. She has been recognized for outstanding contributions in computational protein design, including energy functions, sampling algorithms, and molecules to rewire cellular control circuits. She was an inaugural Chan Zuckerberg Biohub investigator and was inducted into American Institute for Medical and Biological Engineering College of Fellows.
