NAD-COLI K+-UPTAKE PROTEIN TRKA AND SEQUENCE SIMILARITY BETWEEN TRKA AND DOMAINS OF A FAMILY OF DEHYDROGENASES SUGGEST A ROLE FOR NAD+ IN BACTERIAL TRANSPORT( BINDING TO THE ESCHERICHIA)

The nucleotide sequence of trkA, a gene encoding a surface component o f the constitutive K+-uptake systems TrkG and TrkH from Escherichia co li, was determined. The structure of the TrkA protein deduced from the nucleotide sequence accords with the view that TrkA is peripherally b ound to the inner side of the cytoplasmic membrane. Analysis by a dot matrix revealed that TrkA is composed of similar halves. The N-termina l part of each TrkA haff (residues 1-130 and 234-355, respectively) is similar to the complete NAD+-binding domain of NAD+-dependent dehydro genases. The C-terminal part of each TrkA haff (residues 131-233 and 3 57-458, respectively) aligns with the first 100 residues of the cataly tic domain of glyceraldehyde-3-phosphate dehydrogenase. Strong u.v. il lumination at 252nm led to cross-linking of NAD+ or NADH, but not of A TP to the isolated TrkA protein.