Dynamic molecular modeling pathogenic mutations spectrin self-association domain

Disruption of spectrin self-association underlies many inherited hemolytic disorders. Using dynamic modeling and energy minimization, the 3-dimensiona l structure of the self-association domain has been estimated in human eryt hrocyte spectrin and the structural consequences of 17 elliptogenic mutatio ns determined. The predicted structure of the normal self-association domai n was remarkably similar to the crystal structure of the Drosophila a-spect rin 14th repeat unit, despite replacement in the human sequence of over 70% of the amino acids relative to fly spectrin, including 2 prolines in the h uman sequence that appear in helical regions of the fly structure. The pred icted structure placed all hydrophilic residues at the surface and identifi ed 4 salt bridges, 9 hydrophobic interactions, and 4 H-bonds that stabilize the native self-association unit. Remarkably, every pathologic point mutat ion, including seemingly conservative substitutions such as G for A, A for V, or K for R (single-letter amino acid codes), led to conformational rearr angements in the predicted structure. The degree of structural disruption, as measured by root-mean-square deviation of the predicted backbone structu re from the Drosophila structure, correlated strongly with the severity of clinical disease associated with each mutation. This approach thus enables an accurate prediction, from the primary sequence, of the clinical conseque nces of specific point mutations in spectrin. The 3-dimensional structure o f the self-association domain derived here is likely to be accurate. It pro vides a powerful heuristic model for understanding how point mutations disr upt cytoskeletal function in a variety of hemolytic disorders. (C) 2001 by The American Society of Hematology.