The heterologous expression of functional mammalian integral membrane proteins still represents a significant hurdle towards evaluating the relationship between their structure and function. We have therefore utilised the OmpA signal sequence to deliberately target the expression of a mammalian nucleotide sugar transporter, the murine CMP-sialic acid transporter, to the E. coli inner membrane. The functionality of the recombinant CMP-sialic acid transporter could then be evaluated either following the spheroplasting of E. coli cells or through the isolation of the E. coli inner membrane and the formation of mixed phosphatidylcholine-inner membrane proteoliposomes.