The self-catalytic protein splicing mechanism is mediated by the intein plus the first amino acid following the intein C-terminus (termed the +1 residue). Although polymorphisms of conserved residues elsewhere in inteins have been widely reported, no splicing-competent intein has been observed without a Ser, Thr or Cys in this functionally essential +1 position. This residue is the nucleophile in two steps of the protein splicing pathway: ligation of the extein fragments during transesterification and formation of a peptide bond between the exteins by an acyl rearrangement. An intein-like element in a hypothetical protein (gene Magn8951) from Magnetospirillum magnetotacticum has all intein signature sequences except the +1 residue, where it has a Tyr. Although the Tyr side-chain hydroxyl can potentially mediate the transesterification reaction, an acyl shift has never been observed with this residue. When the activities of this bacterial intein-like element were studied, protein splicing was not observed and N-terminal cleavage predominated. Mutation of Tyr+1 to Phe or Ala indicated that the Tyr side-chain hydroxyl was not necessary for N-terminal cleavage. Protein splicing activity could be rescued by ‘reversion’ of Tyr+1 to Cys.
Conference Article| April 01 2004
Rescue of protein splicing activity from a Magnetospirillum magnetotacticum intein-like element
Biochem Soc Trans (2004) 32 (2): 250-254.
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M.W. Southworth, J. Yin, F.B. Perler; Rescue of protein splicing activity from a Magnetospirillum magnetotacticum intein-like element. Biochem Soc Trans 1 April 2004; 32 (2): 250–254. doi: https://doi.org/10.1042/bst0320250
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