Calmodulin binding properties of peptide analogues and fragments of the calmodulin‐binding domain of simian immunodeficiency virus transmembrane glycoprotein 41

Abstract The calcium‐regulatory protein calmodulin (CaM) can bind with high affinity to a region in the cytoplasmic C‐terminal tail of glycoprotein 41 of simian immunodeficiency virus (SIV). The amino acid sequence of this region is 1 DLWETLRRGGRW 13 ILAIPRRIRQGLELT 28 L. In this work, we have used near‐ and far‐uv CD, and fluorescence spectroscopy, to study the orientation of this peptide with respect to CaM. We have also studied biosynthetically carbon‐13 methyl‐Met calmodulin by 1 H, 13 C heteronuclear multiple quantum coherence NMR spectroscopy. Two Trp‐substituted peptides, SIV‐W3F and SIV‐W12F, were utilized in addition to the intact SIV peptide. Two half‐peptides, SIV‐N (residues 1–13) and SIV‐C (residues 13–28) were also synthesized and studied. The spectroscopic results obtained with the SIV‐W3F and SIV‐W12F peptides were generally consistent with those obtained for the native SIV peptide. Like the native peptide, these two analogues bind with an α‐helical structure as shown by CD spectroscopy. Fluorescence intermolecular quenching studies suggested binding of Trp3 to the C‐lobe of CaM. Our NMR results show that SIV‐N can bind to both lobes of calcium‐CaM, and that it strongly favors binding to the C‐terminal hydrophobic region of CaM. The SIV‐C peptide binds with relatively low affinity to both halves of the protein. These data reveal that the intact SIV peptide binds with its N‐terminal region to the carboxy‐terminal region of CaM, and this interaction initiates the binding of the peptide. This orientation is similar to that of most other CaM‐binding domains. © 2000 John Wiley & Sons, Inc. Biopoly 58: 50–62, 2001