Tyrosylprotein sulfotransferase is an enzyme that catalyzes

tyrosine sulfation Tyrosine sulfation is a posttranslational modification where a sulfate group is added to a tyrosine residue of a protein molecule. Secreted proteins and extracellular parts of membrane proteins that pass through the Golgi apparatus may be sulfated. ...

Function

Tyrosylprotein sulfotransferase is the enzyme that catalyzes the

sulfation Sulfation is the chemical reaction that entails the addition of SO3 group. In principle, many sulfations would involve reactions of sulfur trioxide (SO3). In practice, most sulfations are effected less directly. Regardless of the mechanism, the ...

reaction of protein tyrosines, a

post-translational modification Post-translational modification (PTM) is the covalent and generally enzymatic modification of proteins following protein biosynthesis. This process occurs in the endoplasmic reticulum and the golgi apparatus. Proteins are synthesized by ribos ...

of proteins. It utilizes 3'-Phosphoadenosine-5'-phosphosulfate (PAPS) as the

sulfonate In organosulfur chemistry, a sulfonate is a salt or ester of a sulfonic acid. It contains the functional group , where R is an organic group. Sulfonates are the conjugate bases of sulfonic acids. Sulfonates are generally stable in water, non-o ...

donor and binds proteins with target tyrosine residues to eventually form the tyrosine O-sulfate ester group and the desulfonated 3’-phosphoadenosine-5’-phosphate (PAP). TPST and tyrosine sulfation is involved in a large number of biological and physiological processes. Tyrosine sulfation has been found to be an important part of the inflammatory process, leukocyte movement and cytosis, viral cell entrance, and other cell-cell and protein-protein interactions. Selection for specific tyrosine residues requires a generally accessible tyrosine residue, and acidic residues within +5 or -5 residues of the target tyrosine.

P-selectin glycoprotein ligand-1 Selectin P ligand, also known as SELPLG or CD162 (cluster of differentiation 162), is a human gene. SELPLG codes for PSGL-1, the high affinity counter-receptor for P-selectin on myeloid cells and stimulated T lymphocytes. As such, it plays a crit ...

(PSGL-1) has been extensively studied as a substrate for TPST and the importance of sulfation in PSGL-1 and its ability to bind its receptor. Another substrate for TPST, CC-chemokine Receptor 5 (

CCR5 C-C chemokine receptor type 5, also known as CCR5 or CD195, is a protein on the surface of white blood cells that is involved in the immune system as it acts as a receptor for chemokines. In humans, the ''CCR5'' gene that encodes the CCR5 p ...

), has generated interest because of its role as the target protein for the viral entrance of HIV into cells. The importance of CCR5’s sulfation for

HIV The human immunodeficiency viruses (HIV) are two species of ''Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immune ...

invasion has led to research on TPST and CCR5, including a characterization of the pattern of sulfation of CCR5. Beyond these two proteins, other notable protein substrates include

Cholecystokinin Cholecystokinin (CCK or CCK-PZ; from Greek ''chole'', "bile"; ''cysto'', "sac"; ''kinin'', "move"; hence, ''move the bile-sac (gallbladder)'') is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat an ...

(CCK),

Factor V Factor V (pronounced factor five) is a protein of the coagulation system, rarely referred to as proaccelerin or labile factor. In contrast to most other coagulation factors, it is not enzymatically active but functions as a cofactor. Deficienc ...

and

Factor VIII Factor VIII (FVIII) is an essential blood-clotting protein, also known as anti-hemophilic factor (AHF). In humans, factor VIII is encoded by the ''F8'' gene. Defects in this gene result in hemophilia A, a recessive X-linked coagulation disorder ...

, gastrin, the leech enzyme

hirudin Hirudin is a naturally occurring peptide in the salivary glands of blood-sucking leeches (such as '' Hirudo medicinalis'') that has a blood anticoagulant property. This is fundamental for the leeches’ habit of feeding on blood, since it keeps ...

fibrinogen Fibrinogen (factor I) is a glycoprotein complex, produced in the liver, that circulates in the blood of all vertebrates. During tissue and vascular injury, it is converted enzymatically by thrombin to fibrin and then to a fibrin-based blood cl ...

Complement component 4 Complement component 4 (C4), in humans, is a protein involved in the intricate complement system, originating from the human leukocyte antigen (HLA) system. It serves a number of critical functions in immunity, tolerance, and autoimmunity with ...

, follicle-stimulating hormone receptor (FSHR), and other

chemokine Chemokines (), or chemotactic cytokines, are a family of small cytokines or signaling proteins secreted by cells that induce directional movement of leukocytes, as well as other cell types, including endothelial and epithelial cells. In additio ...

and

G-protein coupled receptors G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptors, and G protein-linked receptors (GPLR), form a large group of protein family, evolution ...

. A full, up-to-date list can be found a
UniProtKB

Characterization and properties

Tyrosylprotein sulfotransferase (TPST) is a type II

transmembrane protein A transmembrane protein (TP) is a type of integral membrane protein that spans the entirety of the cell membrane. Many transmembrane proteins function as gateways to permit the transport of specific substances across the membrane. They frequent ...

. It consists of a short cytosolic region that contains the N-terminus of the protein, a single transmembrane region of about 17 amino acids in length, a small stem region of about 40 amino acids in length, and a larger, catalytic region that is located on the luminal side of the membrane. It is localized to the

Golgi apparatus The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. Part of the endomembrane system in the cytoplasm, it packages proteins into membrane-bound vesicles ...

, specifically in the ''trans''-Golgi region, and acts almost exclusively on secretory and plasma membrane proteins. TPST is about 50-54 kD in size, and has two confirmed

isoform A protein isoform, or "protein variant", is a member of a set of highly similar proteins that originate from a single gene or gene family and are the result of genetic differences. While many perform the same or similar biological roles, some iso ...

s in mammals, TPST-1 and TPST-2, that are 370 and 377 residues in length, respectively. Both are quite similar with an approximately 63% amino acid identity, but show slightly different protein substrate specificities. TPST is a prevalent enzyme, found in many multicellular eukaryotes including mammals, most vertebrates, and a number of invertebrate species as well, including ''

Drosophila melanogaster ''Drosophila melanogaster'' is a species of fly (the taxonomic order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the " vinegar fly" or "pomace fly". Starting with ...

''. Its importance can be further demonstrated by the fact as much as 1% of all secreted and membrane tyrosine residues are found to be sulfated.

Mechanism

Within the last two years, using the crystallized structure of the catalytic region of TPST-2 and different experiments other methods using mass spectrometry methods have come to propose two separate mechanisms.

Two-site ping-pong mechanism

A two-site ping-pong mechanism for TPST and the tyrosine sulfating has been proposed. PAPS enters one site of TPST and the sulfonate group is transferred to a Histidine residue in the enzyme and PAP is release. Then, the target protein and tyrosine bind TPST and the histidine transfers the sulfonate group to the target tyrosine.

SN2-like in-line displacement mechanism

Based on crystal structure of TPST-2 with C4 complement and PAP, an

SN2 The SN2 reaction is a type of reaction mechanism that is common in organic chemistry. In this mechanism, one bond is broken and one bond is formed in a concerted way, i.e., in one step. The name SN2 refers to the Hughes-Ingold symbol of the ...

-like in-line displacement mechanism has been proposed. In this mechanism, both PAPS and the target tyrosine bind to the same active site in the enzyme and are orientated in a way such that a glutamic acid residue acts as a catalytic base on the tyrosine hydroxyl group, an arginine residue acts as a catalytic acid, and serine and lysine residues are used to stabilize the SN2-like intermediate. The deprotonated hydroxyl would attack the sulfonate group, then displace the phosphate group and PAP would be released, along with the sulfotyrosine residue.

Function

Characterization and properties

Mechanism

Two-site ping-pong mechanism

SN2-like in-line displacement mechanism

Examples

See also

References

External links