This is the central core domain found in GerD from a thermophilic Bacillus. GerD plays a critical role in nutrient receptor-mediated spore germination in Bacillus species. The crystal structure of GerD reveals this domain as a trimeric superhelical rope fold. Alterations in GerD structure have profound effects on spores' nutrient germination [1].

1: Structural and functional analysis of the GerD spore germination protein of Bacillus species. Li Y, Jin K, Ghosh S, Devarakonda P, Carlson K, Davis A, Stewart KA, Cammett E, Pelczar Rossi P, Setlow B, Lu M, Setlow P, Hao B; J Mol Biol. 2014;426:1995-2008. PMID:24530795