Sequence determinants of the energetics of folding of a transmembrane four-helix-bundle protein.
Although previous studies are beginning to point to the specific types of helix-helix interactions that stabilize the folds of membrane-bound helical proteins, quantitative thermodynamic data on natural membrane proteins has been very limited. Here the database is expanded substantially by adding thermodynamic data for a series of sequence variants of M2 protein from influenza A virus. The M2 protein has a single transmembrane helix that homotetramerizes to form proton-selective channels that are essential to virus function. To determine the contributions of specific residues to the folding of this protein, a series of transmembrane peptides with single-site changes near the core of the protein were studied by using sedimentation equilibrium analytical ultracentrifugation. Remarkably, a large number of the mutations increased the stability of the protein. The free energies of tetramerization of the variants can be understood in terms of current models for the structure of the protein. In general, the energetic consequences of the mutations are smaller than those observed for similar mutations in water-soluble proteins. This observation is consistent with previous studies and hence may represent a general phenomenon.
Howard
Kathleen P
KP
Department of Chemistry, Swarthmore College, Swarthmore, PA 19081, USA. khoward1@swarthmore.edu
Lear
James D
JD
DeGrado
William F
WF
D000595:Amino Acid Sequence; D002942:Circular Dichroism; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017510:Protein Folding; D017386:Sequence Homology, Amino Acid; D014461:Ultracentrifugation; D014763:Viral Matrix Proteins / Q000737:chemistry*; D000086082:Viroporin Proteins
D014763:Viral Matrix Proteins; C031540:M-protein, influenza virus; C488937:M2 protein, Influenza A virus; D000086082:Viroporin Proteins