This is the middle domain found in DR2241, a multi-domain protein with an N-terminal cobalamin (vitamin B12) chelatase domain. DR2241 is found in D. radiodurans. The middle domain has four alpha-helices (alpha7-alpha10) in contact with the N-terminal domains and C-terminal domain and five anti-parallel beta-strands with strand order 12354 at the outer side of one monomer. The middle domain, as well as the C-terminal domain, are heavily involved in the tetramer stabilisation [1].

1: The crystal structure of DR2241 from Deinococcus radiodurans at 1.9 A resolution reveals a multi-domain protein with structural similarity to chelatases but also with two additional novel domains. Leiros HK, McSweeney SM; J Struct Biol. 2007;159:92-102. PMID:17448684