Structural analysis of sickle hemoglobin fibers

Abstract

We have used helical reconstruction and electron density modeling techniques in our analysis of the structure of sickle hemoglobin (HbS) fibers. The formation of HbS fibers in red blood cells under conditions of deoxygenation is responsible for the clinical manifestations of sickle cell disease. Fibers have a helical pitch of about 2700 Å and an average diameter of about 210 Å. The subunit of structure in fibers consists of two half-staggered strands of HbS molecules termed double strands. Double strands in fibers are oriented such that the axis of the constituent double strands is nearly parallel to the particle axis, as indicated by the optical diffraction pattern of these particles.The pitch of fibers varies from particle to particle, as well as within a single fiber, and this presents special problems in the structural analysis. We have measured the distances corresponding to 180° of rotation in 245 fibers.