Research article

Plant-like substitutions in the large-subunit carboxy terminus of Chlamydomonas Rubisco increase CO₂/O₂ Specificity

Sriram Satagopan^1,3 and Robert J Spreitzer²

¹  Department of Microbiology, Ohio State University, Columbus, OH 43210, USA

²  Department of Biochemistry, University of Nebraska, Lincoln, NE 68588-0664, USA

³  DuPont Knowledge Center, ICICI Knowledge Park, Hyderabad 500078, India

author email corresponding author email

BMC Plant Biology 2008, 8:85doi:10.1186/1471-2229-8-85

Published:	30 July 2008

Abstract

Background

Ribulose-1,5-bisphosphate is the rate-limiting enzyme in photosynthesis. The catalytic large subunit of the green-algal enzyme from Chlamydomonas reinhardtii is ~90% identical to the flowering-plant sequences, although they confer diverse kinetic properties. To identify the regions that may account for species variation in kinetic properties, directed mutagenesis and chloroplast transformation were used to create four amino-acid substitutions in the carboxy terminus of the Chlamydomonas large subunit to mimic the sequence of higher-specificity plant enzymes.

Results

The quadruple-mutant enzyme has a 10% increase in CO₂/O₂ specificity and a lower carboxylation catalytic efficiency. The mutations do not seem to influence the protein expression, structural stability or the function in vivo.

Conclusion

Owing to the decreased carboxylation catalytic efficiency, the quadruple-mutant is not a "better" enzyme. Nonetheless, because of its positive influence on specificity, the carboxy terminus, relatively far from the active site, may serve as a target for enzyme improvement via combinatorial approaches.