Comparative Analysis of 126 Cyanobacterial Genomes Reveals Evidence of Functional Diversity Among Homologs of the Redox-Regulated CP12 Protein    

Abstract

CP12 is found almost universally among photosynthetic organisms, where it plays a key role in regulation of the Calvin cycle by forming a ternary complex with glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and phosphoribulokinase. Newly available genomic sequence data for the phylum Cyanobacteria reveals a heretofore unobserved diversity in cyanobacterial CP12 proteins. Cyanobacterial CP12 proteins can be classified into eight different types based on primary structure features. Among these are CP12-CBS (for cystathionine-b-synthase) domain fusions. CBS domains are regulatory modules for a wide range of cellular activities; many of these bind adenine nucleotides through a conserved motif that is also present in the CBS domains fused to CP12. In addition, a survey of expression data sets shows that the CP12 paralogs are differentially regulated. Furthermore, modeling of the cyanobacterial CP12 protein variants based on the recently available three-dimensional structure of the canonical cyanobacterial CP12 in complex with GAPDH suggests that some of the newly identified cyanobacterial CP12 types are unlikely to bind to GAPDH. Collectively these data show that, as is becoming increasingly apparent for plant CP12 proteins, the role of CP12 in cyanobacteria is likely more complex than previously appreciated, possibly involving other signals in addition to light. Moreover, our findings substantiate the proposal that this small protein may have multiple roles in photosynthetic organisms.

Regulation of photosynthetic carbon metabolism in aquatic and terrestrial organisms by Rubisco activase, redox-modulation and CP12

“…The expression of different CP12s in non-photosynthetic tissues in A. thaliana supports this conclusion (Singh et al, 2008). In cyanobacteria, modeling of CP12 protein variants based on the three-dimensional structure of the canonical cyanobacterial CP12/GAPDH interaction clearly indicates that some of the newly identified CP12 proteins are not likely to bind to GAPDH (Stanley et al, 2013).…”

“…A CP12-like protein also occurs in diatoms where it plays a similar role for the GAPDH found in this organism (Gontero and Maberly, 2012). A second pair of Nterminal cysteine residues is conserved in most CP12 proteins, but is absent in some photosynthetic organisms, e.g., in rhodophytes, Cyanophora and the cyanobacterium, Synechococcus Stanley et al, 2013). Among cyanobacterial CP12 proteins, are three CP12-CBS, containing a CBS (cystathionine-␤-synthase) domain that is fused to CP12.…”

“…As mentioned above, cyanobacteria possess variants of CP12 and those variants are differentially expressed under different conditions (Stanley et al, 2013). Under constant light and in response to a shift from high to low atmospheric CO 2 , the two S. elongatus CP12 proteins, CP12-C lacking the N-terminal disulphide bridge and the canonical CP12 with the two disulphide bridges (CP12-N/C) showed differences in overall expression (Schwarz et al, 2011;Vijayan et al, 2011).…”

“…The 8 types differ in the placement of disulphide bridges, either at the N-or, C-terminus or at both positions (Stanley et al, 2013). Interestingly, one type of cyanobacterial CP12, present in all marine picoplanktonic cyanobacteria, is missing the canonical AWD VEEL core sequence that was considered to be the hallmark of all CP12s Stanley et al, 2013).…”

Engineering cyanobacteria for industrial products

“…Most of the systems currently used to genetically manipulate cyanobacteria can be traced back to the 1970s and 1980s, when the first unicellular and filamentous strains were engineered to perform mutational analyses (Table 19.1). Since the time of these early studies, there have been very important new developments, namely the extensive sequencing of the genomes of different cyanobacterial strains (e.g., Shih et al, 2013;Stanley, Raines, and Kerfeld, 2013) (Mitschke et al, 2011a, b). Therefore, the potential of genetic engineering in cyanobacteria is nowadays widely acknowledged (Ducat, Way, and Silver, 2011).…”