TY  - JOUR
A1  - Hackenberg, Claudia
A1  - Hakanpaeae, Johanna
A1  - Cai, Fei
A1  - Antonyuk, Svetlana
A1  - Eigner, Caroline
A1  - Meissner, Sven
A1  - Laitaoja, Mikko
A1  - Janis, Janne
A1  - Kerfeld, Cheryl A.
A1  - Dittmann, Elke
A1  - Lamzin, Victor S.
T1  - Structural and functional insights into the unique CBS-CP12 fusion protein family in cyanobacteria
JF  - Proceedings of the National Academy of Sciences of the United States of America
N2  - Cyanobacteria are important photosynthetic organisms inhabiting a range of dynamic environments. This phylum is distinctive among photosynthetic organisms in containing genes encoding uncharacterized cystathionine beta-synthase (CBS)-chloroplast protein (CP12) fusion proteins. These consist of two domains, each recognized as stand-alone photosynthetic regulators with different functions described in cyanobacteria (CP12) and plants (CP12 and CBSX). Here we show that CBS-CP12 fusion proteins are encoded in distinct gene neighborhoods, several unrelated to photosynthesis. Most frequently, CBS-CP12 genes are in a gene cluster with thioredoxin A (TrxA), which is prevalent in bloom-forming, marine symbiotic, and benthic mat cyanobacteria. Focusing on a CBS-CP12 from Microcystis aeruginosa PCC 7806 encoded in a gene cluster with TrxA, we reveal that the domain fusion led to the formation of a hexameric protein. We show that the CP12 domain is essential for hexamerization and contains an ordered, previously structurally uncharacterized N-terminal region. We provide evidence that CBS-CP12, while combining properties of both regulatory domains, behaves different from CP12 and plant CBSX. It does not form a ternary complex with phosphoribulokinase (PRK) and glyceraldehyde-3-phosphate dehydrogenase. Instead, CBS-CP12 decreases the activity of PRK in an AMP-dependent manner. We propose that the novel domain architecture and oligomeric state of CBS-CP12 expand its regulatory function beyond those of CP12 in cyanobacteria.
KW  - crystal structure
KW  - hexamer
KW  - redox
KW  - Microcystis aeruginosa
Y1  - 2018
U6  - https://doi.org/10.1073/pnas.1806668115
SN  - 0027-8424
VL  - 115
IS  - 27
SP  - 7141
EP  - 7146
PB  - National Acad. of Sciences
CY  - Washington
ER  -