A common channel-forming motif in evolutionarily distant porins. |
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Authors: | R A Pauptit T Schirmer J N Jansonius J P Rosenbusch M W Parker A D Tucker D Tsernoglou M S Weiss G E Schultz |
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Affiliation: | Biocenter, University of Basel, Switzerland. |
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Abstract: | Four new crystal packings of Escherichia coli porins are presented (phosphoporin, maltoporin, and two crystal forms of matrix porin). These were determined by molecular replacement methods using a polyalanine trial model acquired from the refined coordinates of porin from Rhodobacter capsulatus. The successful molecular replacement shows that the dominant motif found in R. capsulatus porin (a 16-stranded antiparallel beta-barrel) also applies to the E. coli porins, despite the lack of significant amino acid sequence homology. A 30 degrees-40 degrees tilt of the beta-strands with respect to the membrane normal was derived from the intensity distributions in the X-ray diffraction patterns for each porin studied, stressing their similarity. In view of the evolutionary distance between enteric and photosynthetic bacteria, the antiparallel beta-barrel may have significance as a basic structural motif for the formation of bacterial membrane channel structures. |
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