Identification of elements of the peptide binding site of DnaK by peptide cross-linking.

We used photocross-linking of peptides to DnaK to identify elements of the peptide binding site of DnaK. We attached a photoactivatable group (N-hydroxysuccinimidyl-4-azido-salicylic acid (NHS-ASA) or N-iodoacetamidobutyl-4-azido-salicylic acid (I-ABASA)) to different positions on peptide C of the vesicular stomatitis virus glycoprotein, 125I-radiolabeled the cross-linker, cross-linked the peptide to DnaK by UV irradiation, and then determined the amino acid residues of DnaK that were cross-linked to the peptide. Limited trypsin digestion of the DnaK-peptide complex revealed that the derivatives modified with photoactivatable cross-linker peptide C cross-linked to a C-terminal fragment of DnaK and that the N-terminal 45-kDa fragment of DnaK was not cross-linked by these modified peptides. The attachment points of the three peptide C derivatives carrying photoactivatable cross-linkers at different locations on the peptide, PepC-ASA, PepC-S7C-ABASA, and PepC-S8C-ABASA, have been identified as Arg-536, Arg-527, and His-541 of DnaK, respectively. Thus all three peptides cross-linked to amino acids located close together in a sequence that includes one end of the long alpha-helix in the NMR-based secondary structure model of the peptide binding domain of Hsp70 family (Morshauser, R., Wang, H., Flynn, G., and Zuiderweg, E. (1995) Biochemistry 34, 6261-6266).