A High-Resolution Crystal Structure of a Psychrohalophilic alpha-Carbonic Anhydrase from Photobacterium profundum Reveals a Unique Dimer Interface

作者：Somalinga Vijayakumar; Buhrman Greg; Arun Ashikha; Rose Robert B; Grunden Amy M^*

来源：PLos One, 2016, 11(12): e0168022.

DOI：10.1371/journal.pone.0168022

Bacterial alpha-carbonic anhydrases (alpha-CA) are zinc containing metalloenzymes that catalyze the rapid interconversion of CO2 to bicarbonate and a proton. We report the first crystal structure of a pyschrohalophilic alpha-CA from a deep-sea bacterium, Photobacterium profundum. Size exclusion chromatography of the purified P. profundum alpha-CA (PprCA) reveals that the protein is a heterogeneous mix of monomers and dimers. Furthermore, an "in-gel" carbonic anhydrase activity assay, also known as protonography, revealed two distinct bands corresponding to monomeric and dimeric forms of PprCA that are catalytically active. The crystal structure of PprCA was determined in its native form and reveals a highly conserved "knot-topology" that is characteristic of alpha-CA's. Similar to other bacterial alpha-CA's, PprCA also crystallized as a dimer. Furthermore, dimer interface analysis revealed the presence of a chloride ion (Cl-) in the interface which is unique to PprCA and has not been observed in any other alpha-CA's characterized so far. Molecular dynamics simulation and chloride ion occupancy analysis shows 100% occupancy for the Cl- ion in the dimer interface. Zinc coordinating triple histidine residues, substrate binding hydrophobic patch residues, and the hydrophilic proton wire residues are highly conserved in PprCA and are identical to other well-studied alpha-CA's.

• 出版日期2016-12-9