Transmembrane domain

Transmembrane domain usually denotes a transmembrane segment of single alpha helix of a transmembrane protein.[1] More broadly, a transmembrane domain is any membrane-spanning protein domain.

Identification of transmembrane helices

Transmembrane helices are visible in structures of membrane proteins determined by X-ray diffraction. They may also be predicted on the basis of hydrophobicity scales. Because the interior of the bilayer and the interiors of most proteins of known structure are hydrophobic, it is presumed to be a requirement of the amino acids that span a membrane that they be hydrophobic as well. However, membrane pumps and ion channels also contain numerous charged and polar residues within the generally non-polar transmembrane segments.

Using hydrophobicity analysis to predict transmembrane helices enables a prediction in turn of the "transmembrane topology" of a protein; i.e. prediction of what parts of it protrude into the cell, what parts protrude out, and how many times the protein chain crosses the membrane.

Transmembrane helices can also be identified in silico using the bioinformatic tool, TMHMM.[2]

Examples
  • Tetraspanins have 4 conserved transmembrane domains.
  • Mildew locus o (mlo) proteins have 7 conserved transmembrane domains that encode alpha helices.[3]

References
  1. Hayley J. Sharpe; Tim J. Stevens; Sean Munro (9 July 2010). "A Comprehensive Comparison of Transmembrane Domains Reveals Organelle-Specific Properties". Cell. 142 (1): 158–169. doi:10.1016/j.cell.2010.05.037. PMC 2928124. PMID 20603021.
  2. Krogh, Anders; Larsson, Björn; von Heijne, Gunnar; Sonnhammer, Erik L.L. "Predicting transmembrane protein topology with a hidden markov model: application to complete genomes11Edited by F. Cohen". Journal of Molecular Biology. 305 (3): 567–580. doi:10.1006/jmbi.2000.4315.
  3. Devoto, Alessandra; Hartmann, H. Andreas; Piffanelli, Pietro; Elliott, Candace; Simmons, Carl; Taramino, Graziana; Goh, Chern-Sing; Cohen, Fred E.; Emerson, Brent C.; Schulze-Lefert, Paul; Panstruga, Ralph (January 2003). "Molecular Phylogeny and Evolution of the Plant-Specific Seven-Transmembrane MLO Family". Journal of Molecular Evolution. 56 (1): 77–88. doi:10.1007/s00239-002-2382-5. ISSN 0022-2844.
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