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Unconventional translation initiation of human trypsinogen 4 at a CUG codon with an N‐terminal leucine
Author(s) -
Németh Attila L.,
Medveczky Péter,
Tóth Júlia,
Siklódi Erika,
Schlett Katalin,
Patthy András,
Palkovits Miklós,
Ovádi Judit,
Tõkési Natália,
Németh Péter,
Szilágyi László,
Gráf László
Publication year - 2007
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2007.05708.x
Subject(s) - trypsinogen , gene isoform , biology , microbiology and biotechnology , transfection , biochemistry , eukaryotic translation , peptide sequence , alternative splicing , serine protease , amino acid , peptide , leucine , trypsin , translation (biology) , gene , protease , messenger rna , enzyme
Summary Chromosomal rearrangements apparently account for the presence of a primate‐specific gene (protease serine 3) in chromosome 9. This gene encodes, as the result of alternative splicing, both mesotrypsinogen and trypsinogen 4. Whereas mesotrypsinogen is known to be a pancreatic protease, neither the chemical nature nor biological function of trypsinogen 4 has been explored previously. The trypsinogen 4 sequence contains two predicted translation initiation sites: an AUG site that codes for a 72‐residue leader peptide on Isoform A , and a CUG site that codes for a 28‐residue leader peptide on Isoform B . We report studies that provide evidence for the N‐terminal amino acid sequence of trypsinogen 4 and the possible mechanism of expression of this protein in human brain and transiently transfected cells. We raised mAbs against a 28‐amino acid synthetic peptide representing the leader sequence of Isoform B and against recombinant trypsin 4. By using these antibodies, we isolated and chemically identified trypsinogen 4 from extracts of both post mortem human brain and transiently transfected HeLa cells. Our results show that Isoform B , with a leucine N terminus, is the predominant (if not exclusive) form of the enzyme in post mortem human brain, but that both isoforms are expressed in transiently transfected cells. On the basis of our studies on the expression of a series of trypsinogen 4 constructs in two different cell lines, we propose that unconventional translation initiation at a CUG with a leucine, rather than a methionine, N terminus may serve as a means to regulate protein expression.