Membrane protein topology: amino acid residues in a putative transmembrane .alpha.-helix of bacteriorhodopsin labeled with the hydrophobic carbene-generating reagent 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine

Identifying Nonpolar Transbilayer Helices in Amino Acid Sequences of Membrane Proteins

“…However, it is important to note that not all polypeptide sequences that contain such features have membrane spanning helices ; some soluble proteins may include fe atures of this kind, (8,16,26,37,41,56,65,97,98). The prediction of helix B has two possible extremes ; that which is preferred on the basis of experimental observation is shown.…”

“…The VSV G protein has a membrane-anchoring sequence of20 amino acids, which has been progressively shortened by genetic modification (1). Shown are the complete deletion oIthe 20 amino acid region (1), and anchoring segments of 8,12,14,16 aqueous pores. In recent years there have been a number of efforts to examine the possible presence of amphiphilic helices that may provide polar pores (17,24,28).…”

“…While the application of the initial scale suggested locations for all seven helices, the current scale more convincingly delineates the existence and positions of helices C and G. Subsequent experiments have been consistent with and thus support the use of the computer-generated model. While the exact sequence locations ofthe helices in the actual structure are not known, a number of recent chemical modification and protease-digestion studies narrow the possible locations substantially (8,16,26,37,41,56,65,97,98). There remains some ambiguity in the precise location of the short loop connecting helices F and G, but the water-accessible portions of the rest of the sequence are well defined.…”

Structural Arrangement of Lens Fiber Cell Plasma Membrane Protein MP20

“…To better understand the possible role of MP20 in the lens fiber cell plasma membrane, affinity-purified MP20 anti-peptide antibodies and the hydrophobic affinity label 3-(trifluoromethyl)-3-(m-["#&I]iodophenyl)diazirine (["#&I]TID) (Brunner et al, 1985 ;Frielle, Brunner and Curthoys, 1982 ;Hoppe, Brunner and Jorgensen, 1984) have been used to investigate the transmembrane arrangement of MP20. While this report supports a transmembrane arrangement of MP20 that comprises four transmembrane segments, one of the previously proposed transmembrane segments may be extra-membranous, located on the cytoplasmic face of the lens fiber cell plasma membrane.…”

Localization of E1–E2 conformational transitions of sarcoplasmic reticulum Ca-ATPase by tryptic cleavage and hydrophobic labeling

“…The previous characterization of tryptic cleavage patterns of the phosphorylated intermediates of Ca-ATPase [1] has been completed by examination of the effect of phosphorylation with Pi-In addition we have studied the exposure of Ca-ATPase in the various conformational states to hydrophobic labeling with the photoactivable reagent trifluoromethyl-[125I]iodophenyldiazirine (TID) 1 [7,17]. Our data indicate that the E1P-EzP transition is accompanied by redistribution of protein mass corresponding to part of the A1 fragment from the cytoplasmic surface to the membrane phase.…”