Results: 4

Fig. 4

Fig. 4. From: A Look at Arginine in Membranes.

The disposition of an arginine in a TM helix. A pathogenic mutation in the single-spanning helix of the receptor tyrosine kinase FGFR3 changes a membrane-embedded glycine to an arginine. The Arg-containing helix stably inserts into the membrane, but the positioning of the mutant arginine is shifted out toward the bilayer interface (Han et al. 2006), consistent with the depth dependence of Arg insertion in the biological hydrophobicity scale

Kalina Hristova, et al. J Membr Biol. ;239(1-2):49-56.
Fig. 1

Fig. 1. From: A Look at Arginine in Membranes.

Physical chemistry of arginine. The side chain of arginine is composed of a hydrophobic propyl moiety and a large, polar, cationic guanidinium group. The resonance-stabilized guanidinium, with a pKa around 12–13, is protonated and cationic under almost all conditions. Nine different atoms in the side chain have significant partial charges, shown on the right. The guanidinium group contains five dipolar N–H protons capable of donating hydrogen bonds and one pair of electrons capable of accepting a hydrogen bond. In terms of the potential for interacting with lipid polar groups, it should be noted that hydrogen bond donor moieties are rare in membranes: Phospholipids provide mostly hydrogen bond acceptor groups, in the form of ester bonds and phosphate oxygens

Kalina Hristova, et al. J Membr Biol. ;239(1-2):49-56.
Fig. 2

Fig. 2. From: A Look at Arginine in Membranes.

Structure of the full-length KvAP potassium channel. This membrane-spanning protein has a tetrameric structure with a central channel domain and four voltage sensor domains on the periphery. The voltage sensor domain contains the critical S4 segment, shown as a red helix. The S4 segment has four arginines, shown in blue, and the arginines are surrounded by a very hydrophobic sequence rich in leucine, isoleucine and phenylalanine residues (top). MacKinnon and others (Jiang et al. 2003a, 2003b) have proposed that the S4 segment responds to changes in TM potential by a paddle-like motion that brings the four arginines deep into the membrane in the so-called down state (upper right). The proposal that a helix with four arginines can be inserted deep into the membrane generated the controversy we discuss in this review (Color figure online)

Kalina Hristova, et al. J Membr Biol. ;239(1-2):49-56.
Fig. 3

Fig. 3. From: A Look at Arginine in Membranes.

The hydrophobicity of arginine in membranes can be expressed in terms of leucine equivalent ratios, or the number of Ala → Leu substitutions required to compensate for a single Ala → Arg substitution. The Wolfenden and GES hydrophobicity scales, based in part on nonpolar solvent partitioning, give high ratios, suggesting that it will be very costly to partition arginine into a membrane. On the other hand, the Kyte–Doolittle, the Wimley–White and the biological hydrophobicity scales yield leucine equivalent ratios for arginine that are much smaller. Scales based on the observed abundance of amino acids in membrane proteins of known structure, shown on the right, generally agree that the cost of inserting arginine in a membrane is not prohibitive, especially when the arginine is not at the center of the bilayer. These results suggest that it should be possible to insert as many as four arginines in a membrane as long as the surrounding residues are sufficiently hydrophobic

Kalina Hristova, et al. J Membr Biol. ;239(1-2):49-56.

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