A few amino acids are post-translationally removed from the C-terminal end of th

Question

A few amino acids are post-translationally removed from the C-terminal end of the beta-lactamase enzyme from B. imaginaries (i.e. - after it is translated and released from the ribosome, a protease chews off a few amino acids). The wild-type enzyme, which has had the amino acids removed from the C'-terminus, is 327 amino acids in length and the C-terminal amino acids are shown below aligned with the C-terminal amino acids of a frameshift mutant, which is not processed at its C-terminus. The wildtype and frameshift mutant have identical coding sequences except for the insertion or deletion of a single nucleotide in the sequences encoding the C-terminal region of the protein. Use this information to answer the questions below. A. What was the mutational event that gave rise to the frameshift mutant? (identify which codon contains the inserted or deleted nucleotide and the position within the codon where the mutation occurred. B. Deduce the number of amino acids in the wild-type enzyme prior to processing of the C-terminus and, as far as possible, the actual sequence of the C-terminus of the wild-type enzyme

Explanation / Answer

A. The mutational event that gave rise to the mutant is insertion of a base in codon after methionine:

Wild type: Amino acid sequence: Asn Met Asn Gly Lys

Coding sequence: AAU AUG AAU GGC AAA

Mutant type: Amino acid sequence: Asn Met Ile Trp Gln Met Cys Asp Met Lys Asp

Coding sequence: AAU AUG AUA UGG CAA AUG UGU GAU AUG AAA GAU

The insertional base is in bold and underlined.

B The number amino acid prior to processing in wild type is 330 amino acids.

The actual sequence is:

Amino acid sequence : Asn Met Asn Gly Lys Cys Val Ile Stop

Coding Sequence: AAU AUG AAU GGC AAA UGU GUG AUA UGA

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