Question

Sequence Comparisons Proteins called molecular chaperones (described in Chapter 4) assist in the process of protein folding. One class of chaperone found in organisms from bacteria to mammals is heat shock protein 90 (Hsp90). All Hsp90 chaperones contain a 10 amino acid "signature sequence," which allows for ready identification of these proteins in sequence databases. Two representations of this signature sequence are shown below. (a) In this sequence, which amino acid residues are invariant (conserved across all species)? (b) At which position(s) are amino acids limited to those with positively charged side chains? For each position, which amino acid is more commonly found? (c) At which positions are substitutions restricted to amino acids with negatively charged side chains? For each position, which amino acid predominates? (d) There is one position that can be any amino acid, although one amino acid appears much more often than any other. What position is this, and which amino acid appears most often?

Answer 1

(a)

Answer

Invariant residues are the amino acids that are identical in all homologue in the protein and they are conserved in all species and are necessary for the structure and functioning of the protein which cannot be replaced by other amino acid residues. In both the sequences of the heat shock protein Hsp 90 the invariant amino acid residues are Y(1), F(7), and R (9).

(b)

Answer

At position 4 and 9 amino acids are limited with Lysine (K) and Arginine (R) respectively which are positively charged. K is more common at position 4 in both the sequences while R is an invariant amino acid residue at position 9 in both sequences.

(c)

Answer

At positions 5 and 10 the substitutions are restricted with amino acid E (Glutamic acid) which has a negative side chain. At both positions the amino acid E is more common and predominant.

(d)

Answer

The position at which any amino acid can be present is position 2. The amino acid which is most common at this position is S (Serine).