Influence of HbCO structure of the bar-headed goose on photolysis thermodynamics as studied by the nanosecond laser-ultrasonic technique.

The bar-headed goose, a specialized high-altitude species, has a capacity for high oxygen uptake from a hypoxic environment. It thus has a higher oxygen affinity than other bird species of lower-altitude environments. Oxygen affinity is determined by molecular structures and genetic mutations of hemoglobin (Hb), which can also influence the coordinating structures and dynamics of oxygen-Hb. To explore the structural differences in Hbs as between high and low altitude species, photolysis dynamic parameters, including quantum yield, enthalpy, and conformational volume changes in carboxy-Hbs (HbCO) for the bar-headed goose and low altitude counterparts (the Chinese goose and chicken) were investigated by the laser pumping-probing technique and photoacoustic calorimetry. Comparing the photolysis results for HbCO of the three species, the enthalpy and conformational volume changes of the bar-headed goose were much smaller than those of the others, although the quantum yields of all three species are similar. To explain the possible mechanisms of these differences, modifications of salt bridges and key residue mutations at the α ß subunit interfaces of the proteins are described and discussed briefly.

Tetragonal Crystal Structure of Mung Bean Inhibitor-porcine Trypsin Complex.

Crystal structure of the mung bean inhibitor-porcine trypsin (1:2) ternary complex in the tetragonal crystal with space group I422 was determined at 0.25nm resolution. 56 residues of the mung bean inhibitor were resolved among which one more residue Pro11 was determined than the previously reported structure in the trigonal crystal of the same complex. The structure of the inhibitor in the tetragonal crystal is similar to that in the trigonal crystal and the complexes in tetragonal crystal is also in packing disorder as in trigonal crystal, i.e., the complexes pack in two orientations Ta : MaMb : Tb and Tb : MbMa : Ta(Ta, Tb=trypsin, Ma, Mb=loop I and loop II of mung bean inhibitor respectively). But there are some differences in the two crystal forms. First, the inhibitor in the tetragonal crystal has no pseudo- beta-sheet structure which the trigonal crystal has. Second, its conformation is somewhat different from that in the trigonal crystal.Analysis showed that the linkage peptides between the two regid domains of the inhibitor were flexible, which also accounted for the formation of different crystal forms of this complex. Moreover, comparing mung bean inhibitor to other Bowman-Birk inhibitors showed that the two double-stranded antiparallel beta-sheets and the reactive binding loops were highly conservative.