Crystal structures of three members (BACOVA_00364 from Bacteroides ovatus, 
BACUNI_03039 from Bacteroides uniformis and BACEGG_00036 from Bacteroides 
eggerthii) of the Pfam domain of unknown function (DUF4488) were determined to 
1.95, 1.66, and 1.81 Å resolutions, respectively. The protein structures adopt 
an eight-stranded, calycin-like, β-barrel fold and bind an endogenous unknown 
ligand at one end of the β-barrel. The amino acids interacting with the ligand 
are not conserved in any other protein of known structure with this particular 
fold. The size and chemical environment of the bound ligand suggest binding or 
transport of a small polar molecule(s) as a potential function for these 
proteins. These are the first structural representatives of a newly defined 
PF14869 (DUF4488) Pfam family.