A protein sequence has twenty consecutive hydrophobic amino acids followed by a few hydrophilic residues and this pattern repeats itself five to…
A protein sequence has twenty consecutive hydrophobic amino acids followed by a few hydrophilic residues and this pattern repeats itself five to seven times. Which kind of a protein is described here?
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Correct Answer: Option B
Explanation
Transmembrane domain prediction from sequence:Alpha-helical transmembrane (TM) domains in integral membrane proteins:• A stretch of ~18–25 consecutive hydrophobic amino acids in an-helical conformation can span the lipid bilayer (~30 Å = 20 residues at 1.5 Å/residue rise).• Each TM helix is typically 20–25 amino acids of predominantly hydrophobic residues (Leu, Ile, Val, Ala, Phe, Met, Trp).• Multiple such hydrophobic stretches (repeats) indicate a MULTI-PASS transmembrane protein.Prediction tools: TMHMM, TMbase, Phobius, HMMTOP.If the sequence shows 5–7 hydrophobic stretches of ~20 aa each, the protein likely has 5–7 TM helices (e.g., a GPCR has 7 TM helices, ion channels have multiple TM repeats).Answer: ~20 consecutive hydrophobic residues = one TM helix; multiple such repeats = multi-pass transmembrane protein.