The crystal structure of auracyanin A at 1.85聽脜 resolution: the structures and functions of auracyanins A and B, two almost identical 鈥渂lue鈥?copper proteins, in the photosynthetic bacterium Chloroflexus aurantiacus
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- 作者：Mihwa Lee ; Melissa C. del Rosario ; Hugh H. Harris ; Robert E. Blankenship ; J. Mitchell Guss and Hans C. Freeman
- 关键词：Auracyanin – ; Chloroflexus – ; Copper protein – ; Crystal structure – ; Photosynthesis
- 刊名：Journal of Biological Inorganic Chemistry
- 出版时间：March, 2009
- 出版年：2009
- 期刊代码：121_0949-8257
- 类别：bio
- 卷：14
- 期：3
- 页码：329-345
- 数据来源：sp
摘要
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 脜 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.