The standard molecular model of the fiber of the sickle hemoglobin (HbS: β6 Glu → Val) has been revised to allow both β6 mutation sites to participate in intermolecular contacts, rather than only one β6 site as previously thought, for four molecules per 14-molecule fiber cross section. This structure accurately predicts the copolymerization of hybridized mixtures of HbS with HbA or HbC (β6 Glu → Lys), which could not be reconciled with prior models in which only half the β6 sites were required for assembly. This model suggests new contacts within the fiber and raises the question of whether these cross-linked double strands could possess added stability important in such processes as nucleation.

Escherichia coli strain LE316 contains a mutation in gyrB that results in the substitution of Val164 to Gly and confers both chlorobiocin resistance and temperature sensitivity. Selection for suppressors of the ts phenotype yielded second-site mutations in GyrB at His38 and Thr157. The properties of proteins bearing these mutations have been characterized, and a mechanism of suppression is proposed based upon structural considerations.

NMR spectroscopic changes as a function of pH in solutions of the pheromone-binding protein of Bombyx mori (BmPBP) show that BmPBP undergoes a conformational transition between pH 4.9 and 6.0. At pH below 4.9 there is a single “acid form” (A), and a homogeneous “basic form” (B) exists at pH above 6.0. Between pH 5 and 6, BmPBP exists as a mixture of A and B in slow exchange on the NMR chemical shift time scale, with the transition midpoint at pH 5.4. The form B has a well-dispersed NMR spectrum, indicating that it represents a more structured, “closed” conformation than form A, which has a significantly narrower chemical shift dispersion. Conformational transitions of the kind observed here may explain heterogeneity reported for a variety of odorant-binding proteins, and it will be of interest to further investigate possible correlations with pH-dependent regulation of ligand binding and release in the biological function of this class of proteins.