User:Ying Zhao/Sandbox
From Proteopedia
It is possible that OspB performs an autoproteolysis. There is a set of three residues found on OspB that resembles the catalytic triad of Serine_Proteases. This "constellation" consists of Thr-166, Arg-162, and Glu-184, which is similar to the catalytic triad residues of the serine protease trypsin, which are Ser-195, His-57, Asp-102 [2].
Threonine and Glutamic acid are found in other catalytic triads of the serine hydrolase family, but argenine seems unlikely to replace histidine as a base because of its higher pKa. There have been studies that have shown that Argenine is essential for other enzymatic functions, such as in the Ser-Arg-Asp triad in cytosolic phospholipase A2 and as a catalytic base in Sortase A. Asn-164 forms an H-bond with Thr-166 and may rearrange to form a putative oxyanion hole with Thr-166 and another unidentified atom if active in the catalysis [1].
It was recently discovered that all antibodies contained Fab portions that catalyzed a reaction between singlet oxygen and water, yielding hydrogen peroxide, ozone, water and hydroxide radicals. Hydrogen peroxide is a toxic oxidative species and might be the product of an ancient mechanism to protect against infection. UV absorption increases the rate for this reaction. B. burgdorferi is especially vulnerable to oxidative damage because its ecological niche is in areas with limited oxygen and its genome does not encode a catalase. This oxidative mechanism might explain why some mABs are bactericidal without the use of complement. [1].
References
- ↑ 1.0 1.1 1.2 Becker M, Bunikis J, Lade BD, Dunn JJ, Barbour AG, Lawson CL. Structural investigation of Borrelia burgdorferi OspB, a bactericidal Fab target. J Biol Chem. 2005 Apr 29;280(17):17363-70. Epub 2005 Feb 15. PMID:15713683 doi:10.1074/jbc.M412842200
- ↑ Hedstrom L. Serine protease mechanism and specificity. Chem Rev. 2002 Dec;102(12):4501-24. PMID:12475199
