Details

Autor(en) / Beteiligte

• Boykins, Robert A.
• Buehler, Paul W.
• Jia, Yiping
• Venable, Richard
• Alayash, Abdu I.

Titel

O-raffinose crosslinked hemoglobin lacks site-specific chemistry in the central cavity: Structural and functional consequences of β93Cys modification

Ist Teil von

• Proteins, structure, function, and bioinformatics, 2005-06, Vol.59 (4), p.840-855

Ort / Verlag

Hoboken: Wiley Subscription Services, Inc., A Wiley Company

Erscheinungsjahr

2005

Quelle

Wiley Online Library - AutoHoldings Journals

Beschreibungen/Notizen

• Reacting human deoxyHbA0 with oxidized raffinose (O‐raffinose), a trisaccharide, results in a low oxygen affinity “blood substitute,” stabilized in a noncooperative T‐conformation and possesses readily oxidizable rhombic heme. In this study, we fractionated the O‐raffinose–modified HbA0 heterogeneous polymer (O‐R‐PolyHbA0) into six distinct fractions with a molecular weight distribution ranging from 64 to ∼600 kDa using size‐exclusion chromatography (SEC). Oxygen equilibrium and kinetics binding parameters of all fractions were nearly identical, reflecting a lack of heterogeneity in ligand binding properties among O‐R‐PolyHbA0 species (Hill coefficient n equal to 1.0). Several mass spectrometry techniques were used to evaluate undigested and digested HbA0, O‐R‐PolyHbA0, and O‐R‐PolyHbA0 fractions. Proposed sites of intramolecular crosslinking (i.e., β1Lys82, β2Lys82, and β1Val1) were not found to be the predominant site of crosslinking within the central cavity. Intermolecular crosslinking with O‐raffinose results in no discernible site of amino acids modifications with the exception of β93Cys and α104Cys. Based on accessible surface area (ASA) calculations in intact deoxyHbA0, slight conformational changes are required to allow for the S on α104Cys to be modified during the reaction with O‐raffinose or its partially oxidized product(s). The stabilization of HbA0 in the T‐conformation may not be a direct correlate of O‐raffinose induced changes, but an indirect consequence of changing hydration in the water‐filled central cavity and/or the distal heme pocket leading in the latter case to accelerated iron oxidation. Structural data presented here when taken together with the oxidative instability of O‐R‐PolyHbA0 may provide some basis for the reported toxicity of this oxygen carrier. Proteins 2005. Published 2005 Wiley‐Liss, Inc.