Question

. Protein X is a single polypeptide with three functional domains. The first is a globular domain which has a protein binding domain and contains both alpha-helices and beta-sheets. The second domain is a group of seven alpha-helices that contain mostly hydrophobic amino acids. The third domain appears to be an enzymatic domain which transfers a phosphate group from ATP to a hydroxyl group on another protein. Postulate the function of this protein and give reasons that support this prediction.

Answer 1

From the above statement about protein X , it can be postulated that protein X is a transmembrane receptor. This transmembrane receptor have 3 domain

1.Extracellular domains:- this domains binds to other protein or ligand. Because this domains have globular flexiy properties due to presence of alpha helix and beta sheets. This secondary structure allows this domains to interact with other extracellular protein.

2. Transmembrane domain:- Generally cell membranes have two layers, and between this two layery, a hydrophobic environment present there. In this X protein a seven alpha helix domains with hydrophobic rich amino acid present. So this domin span the membrane 7 times.

3.Intracellular or Cytosolic domain:- This domains have enzymatic activity, so it always remains at Cytosolic site. This domains can Phosphorylate hydroxyl group of other protein from the trnasfer of phosphate group from ATP.

So this is a seven transmembrane receptor with have Phosphorylate activity. When a extracellular ligand bind with these receptor then Cytosolic domain becomes active and it then initiated downstream signalling pathway in the cell.