Subtilisin

From Wikipedia, the free encyclopedia

Please expand this article.
Further information might be found in a section of the talk page or at Requests for expansion.

Subtilisin
Image:1st2.png Crystal structure of Subtilisin
Gene code:
Structure:
Recent publications:

<tr><td bgcolor=#e7dcc3 width=85>protein type:</td>

   <td style="border-top:1px solid #e7dcc3" width=220>Serine protease</td></tr>

<tr><td bgcolor=#e7dcc3 width=85>Functions:</td>

   <td style="border-top:1px solid #e7dcc3" width=220></td></tr>

<tr><td bgcolor=#e7dcc3 width=85>Domains:</td>

   <td style="border-top:1px solid #e7dcc3" width=220></td></tr>

<tr><td bgcolor=#e7dcc3 width=85>Diseases:</td>

   <td style="border-top:1px solid #e7dcc3" width=220></td></tr>

</table> Subtilisin (serine endopeptidase) is a proteolytic enzyme initially obtained from B. subtilis. It is secreted in large amounts from many Bacillus species.

The structure of subtilisin have been determined by X-ray crystallography. It is a 275 residue globular protein with several alpha-helices, and a large beta-sheet. It is structurally unrelated to the chymotrypsin-clan of serine proteases, but uses the same type of catalytic triad in the active site. This makes it the classic example of convergent evolution.

[edit] Charge-relay Site of Subtilisin

The active site features a charge-relay network involving Asp-32, His-64, and active site Ser-221 arranged in a catalytic triad. The charge-relay network functions as follows: The carboxylate side chain of Asp-32 hydrogen bonds to a nitrogen-bonded proton on His-64's imidazole ring. This is possible because Asp is negatively charged at physiological pH. The other nitrogen on His-64 hydrogen bonds to the O-H proton of Ser-221. This last interaction results in charge-separation of O-H, with the oxygen atom being more nucleophilic. This allows the oxygen atom of Ser-211 to attack incoming substrates (ie. peptide bonds), assisted by a neighboring carboxyamide side chain of Asn-155.

Even though Asp-32, His-64, and Ser-221 are sequentially far apart, they converge in the 3D structure to form the active site.

To summarize the interactions described above, Ser-221 acts as a nucleophile and cleaves peptide bonds with its partially negative oxygen atom. This is possible due to the nature of the charge-relay site of subtilisin.