1thk
|
Effect of Shuttle Location and pH Environment on H+ Transfer in Human Carbonic Anhydrase II
OverviewOverview
In the catalysis of the hydration of carbon dioxide and dehydration of, bicarbonate by human carbonic anhydrase II (HCA II), a histidine residue, (His64) shuttles protons between the zinc-bound solvent molecule and the, bulk solution. To evaluate the effect of the position of the shuttle, histidine and pH on proton shuttling, we have examined the catalysis and, crystal structures of wild-type HCA II and two double mutants: H64A/N62H, and H64A/N67H HCA II. His62 and His67 both have their side chains, extending into the active-site cavity with distances from the zinc, approximately equivalent to that of His64. Crystal structures were, determined at pH 5.1-10.0, and the catalysis of the exchange of (18)O, between CO(2) and water was assessed by mass spectrometry. Efficient, proton shuttle exceeding a rate of 10(5) s(-)(1) was observed for, histidine at positions 64 and 67; in contrast, relatively inefficient, proton transfer at a rate near 10(3) s(-)(1) was observed for His62. The, observation, in the crystal structures, of a completed hydrogen-bonded, water chain between the histidine shuttle residue and the zinc-bound, solvent does not appear to be required for efficient proton transfer. The, data suggest that the number of intervening water molecules between the, donor and acceptor supporting efficient proton transfer in HCA II is, important, and furthermore suggest that a water bridge consisting of two, intervening water molecules is consistent with efficient proton transfer.
DiseaseDisease
Known disease associated with this structure: Osteopetrosis, autosomal recessive 3, with renal tubular acidosis OMIM:[611492]
About this StructureAbout this Structure
1THK is a Single protein structure of sequence from Homo sapiens with ZN as ligand. Active as Carbonate dehydratase, with EC number 4.2.1.1 Full crystallographic information is available from OCA.
ReferenceReference
Structural and kinetic characterization of active-site histidine as a proton shuttle in catalysis by human carbonic anhydrase II., Fisher Z, Hernandez Prada JA, Tu C, Duda D, Yoshioka C, An H, Govindasamy L, Silverman DN, McKenna R, Biochemistry. 2005 Feb 1;44(4):1097-105. PMID:15667203
Page seeded by OCA on Mon Nov 12 19:25:09 2007