GLYCATED HUMAN HEMOGLOBIN (HBA(1C)) - FUNCTIONAL-CHARACTERISTICS AND MOLECULAR MODELING STUDIES

A minor hemoglobin component of human red cell hemolysate, HbA(1c), is the result of the non-enzymatic reaction of glucose with the cu-amino groups of the valine residues at the N-terminus of the beta-chains of human hemoglobin. In this paper, the effect of protons, chloride and 2,3-diphosphoglycerate (DPG) on the functional properties of HbA(1c) h as been investigated in some details. Moreover, the structural modific ations induced on the native molecule by the sugar moieties, studied b y computer modeling, do agree with the observed functional alterations . In particular, the functional results indicate that: (a) the low-aff inity conformation (or T-state) of HbA(1c) is destabilized by the chem ical modification per se; (b) the Bohr effect is reduced with respect to that of native HbA(0); (c) the affinity of the T-state of HbA(1c) f or 2,3-diphosphoglycerate is about 2.6 x lower than that of the corres ponding conformational state of HbA(0), while the R-state is less affe cted with, the affinity being 1.7 x lower. At the structural level, co mputer modeling studies show that the two sugar moieties are asymmetri cally disposed within the 2,3-diphosphoglycerate binding site. In addi tion, molecular mechanics and dynamics calculations concerning the int eraction with 2,3-diphosphoglycerate indicate that while in HbA(0) the effector can assume two different stable orientations, in glycated Hb only one orientation is possible. All together, the results show that glycation of the Val 1 residues of both beta-chains does not impair t he binding of DPG but imposes a different mode of binding by changing the internal geometry of the complex and the surface distribution of t he positive electrostatic potential within the binding pocket. (C) 199 8 Elsevier Science B.V. All rights reserved.