1n29
From Proteopedia
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Crystal structure of the N1A mutant of human group IIA phospholipase A2
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Overview
The human group IIA secreted PLA(2) is a 14 kDa calcium-dependent, extracellular enzyme that has been characterized as an acute phase protein, with important antimicrobial activity and has been implicated in signal, transduction. The selective binding of this enzyme to the phospholipid, substrate interface plays a crucial role in its physiological function. To, study interfacial binding in the absence of catalysis, one strategy is to, produce structurally intact but catalytically inactive mutants. The active, site mutants H48Q, H48N, and H48A had been prepared for the secreted, PLA(2)s from bovine pancreas and bee venom and retained minimal catalytic, activity while the H48Q mutant showed the maximum structural integrity., Preparation of the mutant H48Q of the human group IIA enzyme unexpectedly, produced an enzyme that retained significant (2-4%) catalytic activity, that was contrary to expectations in view of the accepted catalytic, mechanism. In this paper it is established that the high residual activity, of the H48Q mutant is genuine, not due to contamination, and can be seen, under a variety of assay conditions including assays in the presence of, Co(2+) and Ni(2+) in place of Ca(2+). The crystallization of the H48Q, mutant, yielding diffraction data to a resolution of 1.5 A, allowed a, comparison with the corresponding recombinant wild-type enzyme (N1A) that, was also crystallized. This comparison revealed that all of the important, features of the catalytic machinery were in place and the two structures, were virtually superimposable. In particular, the catalytic calcium ion, occupied an identical position in the active site of the two proteins, and, the catalytic water molecule (w6) was clearly resolved in the H48Q mutant., We propose that a variation of the calcium-coordinated oxyanion ("two, water") mechanism involving hydrogen bonding rather than the anticipated, full proton transfer to the histidine will best explain the ability of an, active site glutamine to allow significant catalytic activity.
Disease
Known diseases associated with this structure: Colorectal cancer, sporadic OMIM:[172411]
About this Structure
1N29 is a Single protein structure of sequence from Homo sapiens with CA as ligand. Active as Phospholipase A(2), with EC number 3.1.1.4 Full crystallographic information is available from OCA.
Reference
The crystal structure of the H48Q active site mutant of human group IIA secreted phospholipase A2 at 1.5 A resolution provides an insight into the catalytic mechanism., Edwards SH, Thompson D, Baker SF, Wood SP, Wilton DC, Biochemistry. 2002 Dec 31;41(52):15468-76. PMID:12501175
Page seeded by OCA on Mon Nov 12 18:17:03 2007
