Protein Science, Vol 1, Issue 3 356-362, Copyright © 1992 by Cold Spring Harbor Laboratory Press

ARTICLE

A functional protein hybrid between the glucose transporter and the N-acetylglucosamine transporter of Escherichia coli

U. HUMMEL, C. NUOFFER, B. ZANOLARI and B. ERNI
Present address: Ciba-Geigy, Central Research, CH-4002 Basel, Switzerland.

The glucose and N-acetylglucosamine-specific transporters (II(Glc)/III(Glc) and II(GlcNAc)) of the bacterial phosphotransferase system mediate carbohydrate uptake across the cytoplasmic membrane concomitant with substrate phosphorylation. The two transporters have 40% amino acid sequence identity. Eight chimeric proteins between the two transporters were made by gene reconstruction. All hybrid proteins could be expressed, some inhibited cell growth, and one was active. The active hybrid transporter consists of the transmembrane domain (residues 1-386) of the II(Glc) subunit and the two hydrophilic domains (residues 370-648) of II(GlcNAc). The N-terminal hydrophilic domain of II(GlcNAc) contains the transiently phosphorylated cysteine-412. The hybrid protein is specific for glucose, which indicates that the sugar specificity determinant is in the transmembrane domain and that the cysteine from which the phosphoryl group is transferred to the substrate is not part of the binding site. The protein sequence (LKTPGRED) at which the successful fusion occurred has the characteristic properties of an interdomain oligopeptide linker (Argos, P., 1990, J. Mol. Biol. 211, 943-958).
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