title: The crystal structure of auracyanin A at 1.85 A resolution: the structures and functions of auracyanins A and B, two almost identical "blue" copper proteins, in the photosynthetic bacterium Chloroflexus aurantiacus.
abstract: Auracyanins A and B are two closely similar "blue" copper proteins produced by the filamentous anoxygenic phototrophic bacterium Chloroflexus aurantiacus. Both proteins have a water-soluble 140-residue globular domain, which is preceded in the sequence by an N-terminal tail. The globular domains of auracyanins A and B have sequences that are 38% identical. The sequences of the N-terminal tails, on the other hand, are distinctly different, suggesting that auracyanins A and B occupy different membrane sites and have different functions. The crystal structure of auracyanin A has been solved and refined at 1.85 A resolution. The polypeptide fold is similar to that of auracyanin B (Bond et al. in J Mol Biol 306:47-67, 2001), but the distribution of charged and polar residues on the molecular surface is different. The Cu-site dimensions of the two auracyanins are identical. This is unexpected, since auracyanin A has a shorter polypeptide loop between two of the Cu-binding residues, and the two proteins have significantly different EPR, UV-visible and resonance Raman spectra. The genes for the globular domains of auracyanins A and B have been cloned in a bacterial expression system, enabling purification of large quantities of protein. It is shown that auracyanin A is expressed only when C. aurantiacus cells are grown in light, whereas auracyanin B is expressed under dark as well as light conditions. The inference is that auracyanin A has a function in photosynthesis, and that auracyanin B has a function in aerobic respiration.
authors.affiliation: School of Molecular and Microbial Biosciences, University of Sydney, Sydney, NSW, 2006, Australia.
authors.forename: Mihwa
authors.initials: M
authors.lastname: Lee
authors.forename: Melissa C
authors.initials: MC
authors.lastname: del Rosario
authors.forename: Hugh H
authors.initials: HH
authors.lastname: Harris
authors.forename: Robert E
authors.initials: RE
authors.lastname: Blankenship
authors.forename: J Mitchell
authors.initials: JM
authors.lastname: Guss
authors.forename: Hans C
authors.initials: HC
authors.lastname: Freeman
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D015153:Blotting, Western; D041861:Chloroflexus / Q000737:chemistry* / Q000166:cytology / Q000378:metabolism; D018360:Crystallography, X-Ray; D008667:Metalloproteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010788:Photosynthesis; D016133:Polymerase Chain Reaction; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification; D013057:Spectrum Analysis; D014965:X-Rays
chemical_list: D001426:Bacterial Proteins; D008667:Metalloproteins; D011994:Recombinant Proteins; C073756:auracyanin A protein, bacteria; C073757:auracyanin B-1 protein, bacteria; C073758:auracyanin B-2 protein, bacteria