AF2331-like is a 11-kDa orphan protein of unknown function from Archaeoglobus fulgidus. The structure consists of an alpha + beta fold formed by an unusual homodimer, where the two core beta-sheets are interdigitated, containing strands alternating from both subunits. AF2331 contains multiple negatively charged surface clusters and is located on the same operon as the basic protein AF2330. It is suggested that AF2331 and AF2330 may form a charge-stabilized complex in vivo, though the role of the negatively charged surface clusters is not clear.

1: The crystal structure of the AF2331 protein from Archaeoglobus fulgidus DSM 4304 forms an unusual interdigitated dimer with a new type of alpha + beta fold. Wang S, Kirillova O, Chruszcz M, Gront D, Zimmerman MD, Cymborowski MT, Shumilin IA, Skarina T, Gorodichtchenskaia E, Savchenko A, Edwards AM, Minor W; Protein Sci. 2009;18:2410-2419. PMID:19768810