Sodium/D-glucose cotransporter charge movements involve polar residues.

Amphipathic helices (AHs), a secondary feature found in many proteins, are defined by their structure and by the segregation of hydrophobic and polar residues between two faces of the helix. This segregation allows AHs to adsorb at polar–apolar interfaces such as the lipid surfaces of cellular organelles. Using various examples, we discuss here how variations within this general scheme impart membrane-interacting AHs with different interfacial properties. Among the key parameters are: (i) the size of hydrophobic residues and their density per helical turn; (ii) the nature, the charge, and the distribution of polar residues; and (iii) the length of the AH. Depending on how these parameters are tuned, AHs can deform lipid bilayers, sense membrane curvature, recognize specific lipids, coat lipid droplets, or protect membranes from stress. Via these diverse mechanisms, AHs play important roles in many cellular processes.

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Contribution of charged and polar residues for the formation of the E1–E2 heterodimer from Hepatitis C Virus

Journal of Molecular Modeling ◽

10.1007/s00894-010-0672-1 ◽

2010 ◽

Vol 16 (10) ◽

pp. 1625-1637 ◽

Cited By ~ 8

Author(s):

Siti Azma Jusoh ◽

Christoph Welsch ◽

Shirley W. I. Siu ◽

Rainer A. Böckmann ◽

Volkhard Helms

Keyword(s):

Hepatitis C Virus ◽

Hepatitis C ◽

Polar Residues

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Crystal structure of GCN4-pIQI, a trimeric coiled coil with buried polar residues

Journal of Molecular Biology ◽

10.1006/jmbi.1998.2214 ◽

1998 ◽

Vol 284 (4) ◽

pp. 859-865 ◽

Cited By ~ 64

Author(s):

Debra M Eckert ◽

Vladimir N Malashkevich ◽

Peter S Kim

Keyword(s):

Crystal Structure ◽

Coiled Coil ◽

Polar Residues

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Down-Regulation of Cell Surface Receptors Is Modulated by Polar Residues within the Transmembrane Domain

Molecular Biology of the Cell ◽

10.1091/mbc.11.8.2643 ◽

2000 ◽

Vol 11 (8) ◽

pp. 2643-2655 ◽

Cited By ~ 37

Author(s):

Lolita Zaliauskiene ◽

Sunghyun Kang ◽

Christie G. Brouillette ◽

Jacob Lebowitz ◽

Ramin B. Arani ◽

...

Keyword(s):

Cell Surface ◽

Transmembrane Domain ◽

Gradient Centrifugation ◽

Low Density Lipoprotein ◽

Density Lipoprotein ◽

Surface Proteins ◽

Down Regulation ◽

Surface Receptors ◽

Receptor Complexes ◽

Polar Residues

How recycling receptors are segregated from down-regulated receptors in the endosome is unknown. In previous studies, we demonstrated that substitutions in the transferrin receptor (TR) transmembrane domain (TM) convert the protein from an efficiently recycling receptor to one that is rapidly down regulated. In this study, we demonstrate that the “signal” within the TM necessary and sufficient for down-regulation is Thr11Gln17Thr19 (numbering in TM). Transplantation of these polar residues into the wild-type TR promotes receptor down-regulation that can be demonstrated by changes in protein half-life and in receptor recycling. Surprisingly, this modification dramatically increases the TR internalization rate as well (∼79% increase). Sucrose gradient centrifugation and cross-linking studies reveal that propensity of the receptors to self-associate correlates with down-regulation. Interestingly, a number of cell surface proteins that contain TM polar residues are known to be efficiently down-regulated, whereas recycling receptors for low-density lipoprotein and transferrin conspicuously lack these residues. Our data, therefore, suggest a simple model in which specific residues within the TM sequences dramatically influence the fate of membrane proteins after endocytosis, providing an alternative signal for down-regulation of receptor complexes to the well-characterized cytoplasmic tail targeting signals.

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