Part of the ABC transporter complex YkoCDEF that could transport hydroxymethylpyrimidine (HMP) and/or thiamine. Could also transport other HMP-containing products. Binds thiamine via its HMP moiety. Homodimer in vitro. In vivo, may be a part of an ABC transporter complex which is composed of two ATP-binding proteins (YkoD), two transmembrane proteins (YkoC and YkoE) and a solute-binding protein (YkoF) (Probable).