Structure and function of the putative gamma carbonic anydrase domain of thermosyncechococcus elongatus bp-1

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Authors

Pena, Kerry Lynn

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University of Guelph

Abstract

In 'Thermosynechococcus elongatus BP-1' no identifiable carbonic anhydrase (CA) has been found associated with the [beta]-carboxysome. In this thesis, the atomic resolution x-ray structures of the putative [gamma]-carbonic anhydrase ([gamma]-CA) N-terminal domain of CcmM, TCcmM[Delta]194, from ' T. elongatus BP-1' has been determined from two crystallization conditions. These reveal a trimeric, left-handed [beta]-helical structure that closely resembles the [gamma]-CA from 'Methanosarcina thermophila' (Cam). TCcmM[Delta]194 contains essential active site [gamma]-CA residues which superimpose closely on the Cam structure. Structural differences include a disordered N-terminus, shortened loops in the [beta]-helix, and a partially disordered C-terminal [alpha]-helix. Neither construct was capable of detectable CA activity. Chimeric proteins that substituted the disorder prone [alpha]-helix with the equivalent [alpha]-helix residues from Cam were capable of carbonic anhydrase activity at levels equivalent to other known carbonic anhydrases. This work suggests that the N-terminal portion of the CcmM protein in ' T. elongatus' may be responsible for CA activity in the intact carboxysome.

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Keywords

Thermosyncechococcus elongatus BP-1, putative gamma carbonic anhydrase, beta carboxysome, atomic resolution X-ray, trimeric

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