1.B.14.10.6
Cobalt cation concentration sensitive Btu-like system, Btu1, of 698 aas and 1 N-terminal TMS. It facilitates cobalamin uptake in Anabaena sp. PCC 7120 (Graf et al. 2024).  The regulation by cobalt and cobalamin as well as their uptakes are described for Anabaena sp. PCC 7120, a model filamentous heterocyst-forming cyanobacterium. Anabaena contains at least three cobalamin riboswitches in its genome, for one of which the functionality was confirmed (Graf et al. 2024). Two outer membrane-localized cobalamin TonB-dependent transporters, namely BtuB1 and BtuB2, were identified. BtuB2 is important for fast uptake of cobalamin under conditions with low external cobalt, whereas BtuB1 appears to function in cobalamin uptake under conditions of sufficient cobalt supply. While the general function is comparable, the specific function of the two genes differs and mutants thereof show distinct phenotypes. The uptake of cobalamin depends further on the TonB and a BtuFCD machinery, as mutants of tonB3 and btuD show reduced cobalamin uptake rates.