Part of the tripartite ATP-independent periplasmic (TRAP) transport system SiaPQM that catalyzes unidirectional Na(+)-dependent sialic acid uptake. The complex comprises the extracytoplasmic solute receptor protein SiaP, and the two transmembrane proteins SiaQ and SiaM. SiaQ and SiaM form a tight 1:1 complex. Belongs to the TRAP transporter small permease family.