User:Derek Woolley/Atrolysin A

Article Draft
Atrolysin A (, Crotalus atrox metalloendopeptidase a, hemorrhagic toxin a, Crotalus atrox alpha-proteinase, Crotalus atrox proteinase, bothropasin) is an enzyme. This enzyme catalyses the following chemical reaction


 * Cleavage of Asn3-Gln4, His5-Leu6, His10-Leu11, Ala14-Leu15 and Tyr16-Leu17 in insulin B chain; removes C-terminal Leu from small peptides

This endopeptidase is one of six hemorrhagic toxins in the venom of western diamondback rattlesnake.

Atrolysin A contains a metalloproteinase disintegrin-like domain as well as a cysteine-rich domain. The metalloproteinase disintegrin-like domain has shown an ability to degrade sub-endothelial matrix proteins such as type IV collagen, and fibronectin which is partially responsible for the hemorrhage caused by the toxin. The cysteine-rich domain binds to the alpha-2/beta-1 integrin and causes inhibition of the platelet aggregation pathways that collagen is responsible for. The glycoprotein VI (GPVI) collagen receptor however, does not seem affected by atrolysin A or other snake venom metalloproteinases (SVMP ). Other agonists for platelet formation and aggregation such as adenosine diphosphate (ADP) or pathways mediated by convulxin also do not seem inhibited by the toxin in most organisms.

Research further suggests that in some cases, this enzyme has the potential to inhibit platelet formation with certain pathways that were previously determined that the toxin had no effect on. For example, ADP stimulated aggregation appears to be inhibited by atrolysin A in a study where insect cells were used to express the protein, and the protein was inserted into human blood. When this variant of the protein was inserted into human blood, ADP stimulated platelet aggregation was inhibited. This form of platelet aggregation does not appear inhibited by atrolysin A in other studies. This suggests that there may be an interaction between the disintegrin-like domain, and cysteine-rich domain of atrolysin A and fibrinogen receptor alpha-2b/beta-3 as well as the collagen receptor.

The cysteine-rich domain was shown to have two sequences that cause an interaction which prevents alpha-2/beta-1 integrin expressing K562 cells and platelets from binding to collagen.

Amino Acid Sequence and Protein Structure
The amino acid sequence of atrolysin A is 419 sequences long, and contains ten amino acid positions calcium binding sites between positions 9 and 225, some of these calcium binding sites require carbonyl oxygen. There are also three positions (142, 146, 152) that are used for binding with the enzyme's cofactor, zinc. The active site lies at position 143.

A significant portion of the protein from position 1-190 consists of alpha-helical structures with two shorted helixes between positions 315-340. There are 39 observed disulfide bonds in the protein, all but one of these disulfide bonds occur between positions 157-409. Research suggests that the RSECD cysteine residue at positions 272-276 must be involved in a disulfide bond for the enzyme to have an inhibitory affect on platelet aggregation.

Isozymes
Other atrolysin isozymes (A-F) have been further studied to understand potential methods of treatment against SVMPs. Research has been conducted on the use of medications to treat other diseases such as arthritis, and tumor metastasis as well.

Atrolysin B

Atrolysin C

Atrolysin D

Atrolysin E

Atrolysin F