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J Biol Chem. 2009 Oct 23;284(43):29462-9. doi: 10.1074/jbc.M109.027045. Epub 2009 Aug 25.

A cis-proline in alpha-hemoglobin stabilizing protein directs the structural reorganization of alpha-hemoglobin.

Author information

1
School of Molecular and Microbial Biosciences, University of Sydney, New South Wales 2006, Australia. dagell@mail.usyd.edu.au

Abstract

alpha-Hemoglobin (alphaHb) stabilizing protein (AHSP) is expressed in erythropoietic tissues as an accessory factor in hemoglobin synthesis. AHSP forms a specific complex with alphaHb and suppresses the heme-catalyzed evolution of reactive oxygen species by converting alphaHb to a conformation in which the heme is coordinated at both axial positions by histidine side chains (bis-histidyl coordination). Currently, the detailed mechanism by which AHSP induces structural changes in alphaHb has not been determined. Here, we present x-ray crystallography, NMR spectroscopy, and mutagenesis data that identify, for the first time, the importance of an evolutionarily conserved proline, Pro(30), in loop 1 of AHSP. Mutation of Pro(30) to a variety of residue types results in reduced ability to convert alphaHb. In complex with alphaHb, AHSP Pro(30) adopts a cis-peptidyl conformation and makes contact with the N terminus of helix G in alphaHb. Mutations that stabilize the cis-peptidyl conformation of free AHSP, also enhance the alphaHb conversion activity. These findings suggest that AHSP loop 1 can transmit structural changes to the heme pocket of alphaHb, and, more generally, highlight the importance of cis-peptidyl prolyl residues in defining the conformation of regulatory protein loops.

PMID:
19706593
PMCID:
PMC2785579
DOI:
10.1074/jbc.M109.027045
[Indexed for MEDLINE]
Free PMC Article

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