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Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nm and have an inner diameter between 11 and 15 nm. They are formed by the polymerization of a dimer of two globular proteins, alpha and beta tubulin into protofilaments that can then associate laterally to form a hollow tube, the microtubule. The most common form of a microtubule consists of 13 protofilaments in the tubular arrangement.
A protein phosphatase is a phosphatase enzyme that removes a phosphate group from the phosphorylated amino acid residue of its substrate protein. Protein phosphorylation is one of the most common forms of reversible protein posttranslational modification (PTM), with up to 30% of all proteins being phosphorylated at any given time. Protein kinases (PKs) are the effectors of phosphorylation and catalyse the transfer of a γ-phosphate from ATP to specific amino acids on proteins. Several hundred PKs exist in mammals and are classified into distinct super-families. Proteins are phosphorylated predominantly on Ser, Thr and Tyr residues, which account for 79.3, 16.9 and 3.8% respectively of the phosphoproteome, at least in mammals. In contrast, protein phosphatases (PPs) are the primary effectors of dephosphorylation and can be grouped into three main classes based on sequence, structure and catalytic function. The largest class of PPs is the phosphoprotein phosphatase (PPP) family comprising PP1, PP2A, PP2B, PP4, PP5, PP6 and PP7, and the protein phosphatase Mg2+- or Mn2+-dependent (PPM) family, composed primarily of PP2C. The protein Tyr phosphatase (PTP) super-family forms the second group, and the aspartate-based protein phosphatases the third. The protein pseudophosphatases form part of the larger phosphatase family, and in most cases are thought to be catalytically inert, instead functioning as phosphate-binding proteins, integrators of signalling or subcellular traps. Examples of membrane-spanning protein phosphatases containing both active (phosphatase) and inactive (pseudophosphatase) domains linked in tandem are known, conceptually similar to the kinase and pseudokinase domain polypeptide structure of the JAK pseudokinases. A complete comparative analysis of human phosphatases and pseudophosphatases has been completed by Manning and colleagues, forming a companion piece to the ground-breaking analysis of the human kinome, which encodes the complete set of ~536 human protein kinases.
L-Tyrosine or tyrosine or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group. The word "tyrosine" is from the Greek tyrós, meaning cheese, as it was first discovered in 1846 by German chemist Justus von Liebig in the protein casein from cheese. It is called tyrosyl when referred to as a functional group or side chain. While tyrosine is generally classified as a hydrophobic amino acid, it is more hydrophilic than phenylalanine. It is encoded by the codons UAC and UAU in messenger RNA.
Phenylalanine is an essential α-amino acid with the formula C
9H
11NO
2. It can be viewed as a benzyl group substituted for the methyl group of alanine, or a phenyl group in place of a terminal hydrogen of alanine. This essential amino acid is classified as neutral, and nonpolar because of the inert and hydrophobic nature of the benzyl side chain. The L-isomer is used to biochemically form proteins coded for by DNA. Phenylalanine is a precursor for tyrosine, the monoamine neurotransmitters dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline), and the biological pigment melanin. It is encoded by the codons UUU and UUC.
Pyrroloquinoline quinone (PQQ), also called methoxatin, is a redox cofactor and antioxidant.
DD-transpeptidase is a bacterial enzyme that catalyzes the transfer of the R-L-αα-D-alanyl moiety of R-L-αα-D-alanyl-D-alanine carbonyl donors to the γ-OH of their active-site serine and from this to a final acceptor. It is involved in bacterial cell wall biosynthesis, namely, the transpeptidation that crosslinks the peptide side chains of peptidoglycan strands.
Protein tyrosine phosphatases (EC 3.1.3.48, systematic name protein-tyrosine-phosphate phosphohydrolase) are a group of enzymes that remove phosphate groups from phosphorylated tyrosine residues on proteins:
Tyrosine hydroxylase or tyrosine 3-monooxygenase is the enzyme responsible for catalyzing the conversion of the amino acid L-tyrosine to L-3,4-dihydroxyphenylalanine (L-DOPA). It does so using molecular oxygen (O2), as well as iron (Fe2+) and tetrahydrobiopterin as cofactors. L-DOPA is a precursor for dopamine, which, in turn, is a precursor for the important neurotransmitters norepinephrine (noradrenaline) and epinephrine (adrenaline). Tyrosine hydroxylase catalyzes the rate limiting step in this synthesis of catecholamines. In humans, tyrosine hydroxylase is encoded by the TH gene, and the enzyme is present in the central nervous system (CNS), peripheral sympathetic neurons and the adrenal medulla. Tyrosine hydroxylase, phenylalanine hydroxylase and tryptophan hydroxylase together make up the family of aromatic amino acid hydroxylases (AAAHs).
Aspartoacylase is a hydrolytic enzyme that in humans is encoded by the ASPA gene. ASPA catalyzes the deacylation of N-acetyl-l-aspartate (N-acetylaspartate) into aspartate and acetate. It is a zinc-dependent hydrolase that promotes the deprotonation of water to use as a nucleophile in a mechanism analogous to many other zinc-dependent hydrolases. It is most commonly found in the brain, where it controls the levels of N-acetyl-l-aspartate. Mutations that result in loss of aspartoacylase activity are associated with Canavan disease, a rare autosomal recessive neurodegenerative disease.
Met-enkephalin, also known as metenkefalin (INN), sometimes referred to as opioid growth factor (OGF), is a naturally occurring, endogenous opioid peptide that has opioid effects of a relatively short duration. It is one of the two forms of enkephalin, the other being leu-enkephalin. The enkephalins are considered to be the primary endogenous ligands of the δ-opioid receptor, due to their high potency and selectivity for the site over the other endogenous opioids.
Glutamate carboxypeptidase II (GCPII), also known as N-acetyl-L-aspartyl-L-glutamate peptidase I, NAAG peptidase, or prostate-specific membrane antigen (PSMA) is an enzyme that in humans is encoded by the FOLH1 gene. Human GCPII contains 750 amino acids and weighs approximately 84 kDa.
Carboxypeptidase E (CPE), also known as carboxypeptidase H (CPH) and enkephalin convertase, is an enzyme that in humans is encoded by the CPE gene. This enzyme catalyzes the release of C-terminal arginine or lysine residues from polypeptides.
N-Acetylaspartylglutamic acid is a peptide neurotransmitter and the third-most-prevalent neurotransmitter in the mammalian nervous system. NAAG consists of N-acetylaspartic acid (NAA) and glutamic acid coupled via a peptide bond.
Carboxypeptidase A usually refers to the pancreatic exopeptidase that hydrolyzes peptide bonds of C-terminal residues with aromatic or aliphatic side-chains. Most scientists in the field now refer to this enzyme as CPA1, and to a related pancreatic carboxypeptidase as CPA2.
In enzymology, a steroid Δ5-isomerase is an enzyme that catalyzes the chemical reaction
Tyrosine—tRNA ligase, also known as tyrosyl-tRNA synthetase is an enzyme that is encoded by the gene YARS. Tyrosine—tRNA ligase catalyzes the chemical reaction
Protein tyrosine phosphatase non-receptor type 5 is an enzyme that in humans is encoded by the PTPN5 gene.
A non-receptor tyrosine kinase (nRTK) is a cytosolic enzyme that is responsible for catalysing the transfer of a phosphate group from a nucleoside triphosphate donor, such as ATP, to tyrosine residues in proteins. Non-receptor tyrosine kinases are a subgroup of protein family tyrosine kinases, enzymes that can transfer the phosphate group from ATP to a tyrosine residue of a protein (phosphorylation). These enzymes regulate many cellular functions by switching on or switching off other enzymes in a cell.
Detyrosination is a form of posttranslational modification that occurs on alpha-tubulin. It consists of the removal of the C-terminal tyrosine to expose a glutamate at the newly formed C-terminus. Tubulin polymers, called microtubules, that contain detyrosinated alpha-tubulin are usually referred to as Glu-microtubules while unmodified polymers are called Tyr-microtubules.
Arginylation is a post-translational modification in which proteins are modified by the addition of arginine (Arg) at the N-terminal amino group or side chains of reactive amino acids by the enzyme, arginyltransferase (ATE1). Recent studies have also revealed that hundreds of proteins in vivo are arginylated, proteins which are essential for many biological pathways. While still poorly understood in a biological setting, the ATE1 enzyme is highly conserved which suggests that arginylation is an important biological post-translational modification.
References
- ↑ Argarana CE, Barra HS, Caputto R (January 1980). "Tubulinyl-tyrosine carboxypeptidase from chicken brain: properties and partial purification". Journal of Neurochemistry. 34 (1): 114–8. doi:10.1111/j.1471-4159.1980.tb04628.x. PMID 7452228.
- ↑ Kumar N, Flavin M (July 1981). "Preferential action of a brain detyrosinolating carboxypeptidase on polymerized tubulin". The Journal of Biological Chemistry. 256 (14): 7678–86. doi: 10.1016/S0021-9258(19)69014-9 . PMID 6114100.
- ↑ Arce CA, Barra HS (June 1983). "Association of tubulinyl-tyrosine carboxypeptidase with microtubules". FEBS Letters. 157 (1): 75–8. doi: 10.1016/0014-5793(83)81119-3 . PMID 6862022.
- ↑ Rodriguez de la Vega M, Sevilla RG, Hermoso A, Lorenzo J, Tanco S, Diez A, Fricker LD, Bautista JM, Avilés FX (March 2007). "Nna1-like proteins are active metallocarboxypeptidases of a new and diverse M14 subfamily". FASEB Journal. 21 (3): 851–65. doi: 10.1096/fj.06-7330com . PMID 17244817.
