The complete nucleotide sequences of the Escherichia coli LIV-BP and LS-BP genes. Implications for the mechanism of high-affinity branched-chain amino acid transport

Abstract

The Escherichia coli LIV-I and LS amino acid transport systems are high-affinity, periplasmic, binding protein-dependent systems that utilize the leucine-, isoleucine-, valine-binding protein (LIV-BP) and leucine-specific binding protein (LS-BP), respectively. These two binding proteins (BPs) interact with a common set of membrane proteins to transport branched-chain amino acids into the cytoplasm. The two BP genes are encoded in a regulon at minute 76 of the E. coli chromosome that also contains the genes for the common membrane protein components. We report here the nucleotide and deduced amino acid sequences for the LIV-BP and LS-BP genes and their protein products. Both BPs are encoded with a 23-amino acid signal sequence that is removed when the BPs are secreted into the periplasm. We have examined the pattern of amino acid sequence conservation between the two BP molecules and, by comparison of the predicted secondary structures to the 2.0-A crystal structure of the LIV-BP, have found regions of the BPs that may be involved in membrane protein interaction. We also analyzed the translational efficiency of the two BP mRNAs as determined by their nucleotide sequences.