2h5c: Difference between revisions

[[Image:2h5c.gif|left|200px]]<br /><applet load="2h5c" size="350" color="white" frame="true" align="right" spinBox="true"  

To address questions regarding the mechanism of serine protease catalysis, we have solved two X-ray crystal structures of alpha-lytic protease (alphaLP) that mimic aspects of the transition states: alphaLP at pH 5 (0.82 A resolution) and alphaLP bound to the peptidyl boronic acid inhibitor, MeOSuc-Ala-Ala-Pro-boroVal (0.90 A resolution). Based on these structures, there is no evidence of, or requirement for, histidine-flipping during the acylation step of the reaction. Rather, our data suggests that upon protonation of His57, Ser195 undergoes a conformational change that destabilizes the His57-Ser195 hydrogen bond, preventing the back-reaction. In both structures the His57-Asp102 hydrogen bond in the catalytic triad is a normal ionic hydrogen bond, and not a low-barrier hydrogen bond (LBHB) as previously hypothesized. We propose that the enzyme has evolved a network of relatively short hydrogen bonds that collectively stabilize the transition states. In particular, a short ionic hydrogen bond (SIHB) between His57 Nepsilon2 and the substrate's leaving group may promote forward progression of the TI1-to-acylenzyme reaction. We provide experimental evidence that refutes use of either a short donor-acceptor distance or a downfield 1H chemical shift as sole indicators of a LBHB.

2H5C is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Lysobacter_enzymogenes Lysobacter enzymogenes] with <scene name='pdbligand=SO4:'>SO4</scene> and <scene name='pdbligand=GOL:'>GOL</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Alpha-lytic_endopeptidase Alpha-lytic endopeptidase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=3.4.21.12 3.4.21.12] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=2H5C OCA].  

[[Category: Agard, D A.]]

[[Category: Daugherty, M D.]]

[[Category: Fuhrmann, C N.]]

''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 17:38:29 2008''