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Proteolytic activity of Crocodylus porosus transthyretin protease and role of the terminal polypeptide sequences

Ladda Leelawatwattana^a, Verayuth Praphanphoj^b,c, Porntip Prapunpoj^a,*

 
ABSTRACT:     Human transthyretin (TTR), a recently identified protease, participates in the biology of high density lipoprotein and in the nervous system. In the present study, we determined whether TTR from a non-mammal Crocodylus porosus (crocTTR) has proteolytic activity and whether the N- and C-termini of the TTR polypeptide affect the proteolytic activity. The proteolytic activity of crocTTR and three chimeric crocTTRs: xenoN/crocTTR (crocTTR in which the N-terminal sequence was replaced with that of Xenopus laevis TTR), pigC/crocTTR (crocTTR in which the C-terminal sequence was replaced with that of Sus scrofa TTR), and xenoN/pigC/crocTTR (crocTTR in which the N- and C-terminal sequences were replaced with that of X. laevis TTR and S. scrofa TTR, respectively) were studied and compared. Using either casein or apoAI as a substrate, crocTTR had a lower proteolytic activity than human TTR. Replacing the C-terminal sequence of crocTTR increased the activity (casein: 1008±36 pmol/min; apoAI: 231±43 pmol/min), whereas replacing the N-terminal sequence decreased the activity (casein: 299±26 pmol/min; apoAI: 31.5±2.0 pmol/min). The activity of xenoN/pigC/crocTTR (casein: 502±11 pmol/min; apoAI: 371±23 pmol/min) was higher than those of crocTTR or xenoN/crocTTR, but similar to that of pigC/crocTTR. These results are the first to show the proteolytic activity of reptile TTR, and that the activity is changed when the N- and/or C-terminal amino acid sequences of the TTR subunit are changed.

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* Corresponding author, E-mail: porntip.p@psu.ac.th

Received 31 Jul 2015, Accepted 0 0000