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Leucine Is the Most Stabilizing Aliphatic Amino Acid in the d Position of a Dimeric Leucine Zipper Coiled Coil

1997; American Chemical Society; Volume: 36; Issue: 41 Linguagem: Inglês

10.1021/bi971424h

1943-295X

Jaideep Moitra, László Szilák, Dmitry Krylov, Charles Vinson,

Enzyme Structure and Function

The energetic contribution of seven amino acids in the d position of a dimeric leucine zipper coiled coil structure was measured by determining the thermal stability. The d position contains the conserved leucines found in the leucine zipper. We used a natural bZIP protein as our host−guest system that remains dimeric when a single d position is mutated. We have determined the thermal stability, monitored by circular dichroism, of 14 proteins which indicate that alanine is 4.6 kcal mol-1 per residue less stabilizing than leucine. The similarly sized amino acid isoleucine is 2.9 kcal mol-1 per residue less stabilizing than leucine, suggesting that leucine is well-packed. Model building indicates that the β-branched amino acids isoleucine and valine in the d position produced interhelical clashes between the Cγ2 methyl groups when placed in the favored rotamer conformation. The stabilization by leucine in different d positions is context-dependent; it varies by over 2 kcal mol-1 in the two positions examined. The order of stabilization is L, M, I, V, C, A, and S. Cysteine in the d position can form a disulfide bond which stabilizes the coiled coil.