Linked Life Data

8262942

Source:http://linkedlifedata.com/resource/pubmed/id/8262942

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
36
pubmed:dateCreated
1994-1-27
pubmed:abstractText
The M-->N transition in the photocycle of bacteriorhodopsin involves the transfer of a proton from Asp96 to the retinylidene Schiff base, possibly through a network of hydrogen-bonded amino acid residues and water molecules (Rothschild, K. J., He, Y. W., Sonar, S., Marti, T., and Khorana, H. G. (1992) J. Biol. Chem. 267, 1615-1622). A conformational change of the protein backbone is also observed during this transition. In this work, we have investigated the effects of replacing the residue Thr46, which might be part of this chain, with an aspartic acid. Both Fourier transform infrared and resonance Raman spectroscopy show that the chromophore structure of this mutant (T46D) is normal. However, N formation is accelerated and N decay is significantly slowed compared to wild-type bacteriorhodopsin. This effect causes the N intermediate to accumulate under steady-state illumination thereby facilitating spectroscopic studies under normal pH conditions. Fourier transform infrared difference spectroscopy reveals that like native bacteriorhodopsin, N formation in T46D involves deprotonation of Asp96, reprotonation of the Schiff base, and a change in the backbone secondary structure. However, in contrast to bacteriorhodopsin, bands assigned to the C = O stretch mode of the carboxylic acid group of Asp96 are upshifted by 10 cm-1 reflecting a change in the Asp96 environment and a drop in its effective pKa throughout the photocycle. This change in the pKa can directly account for changes in the photocycle kinetics and indicates that Asp96 deprotonation/protonation are the rate limiting steps in the formation and decay of the N intermediate. By studying the effects of H/D exchange, evidence is found that the backbone structural changes involve transmembrane alpha-helices. It is proposed that these structural changes serve to modulate the local environment and protonation state of Asp96 during the photocycle and are also essential for formation of the proton conducting hydrogen bonded network which functions during Schiff base reprotonation.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Dec
pubmed:issn
0021-9258
pubmed:author
pubmed:issnType
Print
pubmed:day
25
pubmed:volume
268
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
27046-52
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
1993
pubmed:articleTitle
Asp96 deprotonation and transmembrane alpha-helical structural changes in bacteriorhodopsin.
pubmed:affiliation
Physics Department, Boston University, Massachusetts 02215.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, P.H.S., Research Support, U.S. Gov't, Non-P.H.S., Research Support, Non-U.S. Gov't