Date: 12/10/95

Submitted by: Graham Palmer

Question

Is it possible that the binuclear center is reduced in the x-ray structures recently reported by Tsukihara et al (Science 269, 1069 (1995) and Iwata et al (Nature 376 660 (1995). This would explain (i) the absence of the bridging ligand (ii) the geometry at CuB where the three histidines are arranged in a T-shape in the mammalian structure while the bacterial structure might have only two copper ligands. Both geometries are very unusual for a cupric ion, there being no precedent for copper with only two ligands while a T-shaped ligand field has only been observed for the Type II copper of ascorbate oxidase. There are examples for reduction caused by the x-ray beam.

Gary Baker Comments: At 2.8 Angstroms, would the electron density functions of Fe and Cu be sufficiently intense and broad that they would obscure the electron density of a bridge that had a relatively small number of electrons, such as u-oxo? I haven't checked yet, but there should be some crystal structures of Fe-O-Fe proteins. What resolution was needed to resolve out the oxygen? I think Ellie Adman at Seattle might be a person to talk to.
Date: 12/14/95

Submitted by: Graham Palmer

Question

Vassilev et al (PNAS 92 8680 (1995)) report that lys 324 of subunit I from Neurospora is myristoylated on the epsilon amino group. This residue corresponds to Lys-324 of e.g Rhodobacter. It is located near the bottom of helix 8. As the amino group is now an amide does this mean that this lysine is not part of a proton channel?