The crystal structure of the novel snake venom plasminogen activator TSV-PA: a prototype structure for snake venom serine proteinases.
BACKGROUND
Trimeresurus stejnejeri venom plasminogen activator (TSV-PA) is a snake venom serine proteinase that specifically activates plasminogen. Snake venom serine proteinases form a subfamily of trypsin-like proteinases that are characterised by a high substrate specificity and resistance to inhibition. Many of these venom enzymes specifically interfere with haemostatic mechanisms and display a long circulating half-life. For these reasons several of them have commercial applications and are potentially attractive pharmacological tools.


RESULTS
The crystal structure of TSV-PA has been determined to 2.5 A resolution and refined to an R factor of 17.8 (R free, 24.4). The enzyme, showing the overall polypeptide fold of trypsin-like serine proteinases, displays unique structural elements such as the presence of a phenylalanine at position 193, a C-terminal tail clamped via a disulphide bridge to the 99-loop, and a structurally conserved Asp97 residue. The presence of a cis proline at position 218 is in agreement with evolutionary relationships to glandular kallikrein.


CONCLUSIONS
We postulate that Phe 193 accounts for the high substrate specificity of TSV-PA and renders it incapable of forming a stable complex with bovine pancreatic trypsin inhibitor and other extended substrates and inhibitors. Mutational studies previously showed that Asp97 is crucial for the plasminogenolytic activity of TSV-PA, here we identify the conservation of Asp97 in both types of mammalian plasminogen activator - tissue-type (tPA) and urokinase-type (uPA). It seems likely that Asp97 of tPA and uPA will have a similar role in plasminogen recognition. The C-terminal extension of TSV-PA is conserved among snake venom serine proteinases, although its function is unknown. The three-dimensional structure presented here is the first of a snake venom serine proteinase and provides an excellent template for modelling other homologous family members.
Parry
M A
MA
Max-Planck Institute of Biochemistry Department for Structural Research Am Klopferspitz 18a, 82152, Martinsried, Germany parry@biochem.mpg.de
Jacob
U
U
Huber
R
R
Wisner
A
A
Bon
C
C
Bode
W
W
D000590:Amino Acid Chloromethyl Ketones / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D003435:Crotalid Venoms / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000378:metabolism; D006023:Glycoproteins / Q000737:chemistry*; D006801:Humans; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010958:Plasminogen / Q000378:metabolism; D010960:Plasminogen Activators / Q000737:chemistry*; D011487:Protein Conformation; D017510:Protein Folding; D016415:Sequence Alignment; D012697:Serine Endopeptidases
D000590:Amino Acid Chloromethyl Ketones; D003435:Crotalid Venoms; D004791:Enzyme Inhibitors; D006023:Glycoproteins; D046911:Macromolecular Substances; C051330:glutamyl-glycyl-arginine chloromethyl ketone; D010958:Plasminogen; D010960:Plasminogen Activators; D012697:Serine Endopeptidases; C093329:TSV-PA protein, Trimeresurus stejnegeri