Hydrophobic regions sequence lengths

The 4TM receptors are pentameric complexes composed of subunits of 420 to 550 amino acids. The subunits exhibit sequence identities from 25 to 75%, with a similar distribution of hydrophobic and hydrophilic domains (Table 3.1). The hydrophilic 210 to 230 amino-acid N-terminal domain is followed by three closely spaced hydrophobic and putative transmembrane domains, then a variable-length intracellular loop, and finally a fourth putative transmembrane region shortly before the C-terminus (Figure 3.1). Of the four candidate transmembrane regions, evidence suggests that TM2 forms an a-helix, while the other hydrophobic regions more likely are folded as (3-sheets. 

The primary structure of the ADH from L. brevis contains several structures which are typical for short-chain ADHs. The N-terminus, with a length of approximately 30 amino acids, is widely regarded as the coenzyme binding site with the conserved motif G-X-X-X-G-X-G, which is G-G-T-L-G-I-G for Lactobacillus brevis. A second conserved domain found in the L. brems-ADH sequence is a hydrophobic region comprising 10 or 11 residues, respectively. It contains two highly conserved glycines (G82 and G92), separated by nine amino acids. Such structures seem to be located inside the protein and determine the conformation of the enzyme. 

The structure of the hydrophobically modified polymer is set by the number of micelles and the number of hydrophobic monomers present during polymerization. Determination of the structure of the polymer is a problem because of the extremely small concentration of the hydrophobic monomers in the polymer (< 1 mol %). Normal analytical techniques such as NMR are not suflBciently sensitive to determine the number or the sequence length of the hydrophobic regions in such polymers. 

Figure 10.30 Amino acid sequences of the hellx-loop-helix region of some members of the b/HLH and b/HLH/zlp families of transcription factors. Residues that form the hydrophobic core of the four-helix bundle are colored green and a conserved lysine residue is blue. The loop region between HI and H2 is highly variable in length but must be at least four or five residues long.

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