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Calorimetric analyses of the interaction between SecB and its ligands
Author(s) -
Randall Linda L.,
Topping Traci B.,
Suciu Dominic,
Hardy Simon J. S.
Publication year - 1998
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1002/pro.5560070514
Subject(s) - periplasmic space , chaperone (clinical) , cytoplasm , bacterial outer membrane , biochemistry , isothermal titration calorimetry , biology , sequence (biology) , signal peptide , peptide sequence , escherichia coli , membrane protein , biophysics , chemistry , crystallography , membrane , gene , medicine , pathology
Abstract SecB is a chaperone in Escherichia coli dedicated to export of proteins from the cytoplasm to the periplasm and outer membrane. It functions to bind and deliver precursors of exported proteins to the translocation apparatus before they fold into their native structures, thus maintaining them in a competent state for translocation across the membrane. The natural ligands of SecB are precursor proteins containing leader sequences. There are numerous reports in the literature indicating that SecB does not specifically recognize the leader peptides. However, two published investigations have concluded that the leader peptide is the recognition element (Watanabe M, Blobel G. 1989. Cell 58 :685‐705; Watanabe M, Blobel G. 1995. Proc Natl Acad Sci USA 92 :10133‐10136). In this work we use titration calorimetry to show that SecB binds two physiological ligands, which contain leader sequences, with no higher affinity than the same molecules lacking their leader sequences. Indeed, for one ligand the presence of the leader sequence reduces the affinity. Therefore, it can be concluded that the leader sequence provides no positive contribution to the binding energy.