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PubMed · 15574427

Distal substrate interactions enhance plasmepsin activity.

Eva S Istvan·Daniel E Goldberg
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Abstract

Plasmepsin II (PM II) is an aspartic protease active in hemoglobin (Hb) degradation in the protozoan parasite Plasmodium falciparum. A fluorescence-quenched octapeptide substrate based on the initial hemoglobin cleavage site is recognized well by PM II. C-terminal extension of this peptide has little effect, but N-terminal extension results in higher maximal velocity and dramatic concentration-dependent substrate inhibition. This inhibition, but not the rate stimulation, depends on the presence of a DABCYL group on the peptide N terminus. Using site-directed mutagenesis, we have identified PM II residues that interact with N-terminal amino acids of peptide substrates. The same residues influence degradation of Hb by PM II. Cathepsin E (CatE), a related mammalian aspartic protease, is also stimulated by N-terminally extended substrates. This suggests that distal substrate interactions as far out as P6 may be a general property of aspartic proteases and may be important in substrate and inhibitor recognition. Although PM II and CatE are similar in their ability to cleave Hb-based peptides and Hb alpha-chains, CatE is not able to degrade native Hb, which is a substrate for PM II. Based on these results, we propose that PM II may have the special feature of being a Hb denaturase.

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Amino Acid SequenceAnimalsAspartic Acid EndopeptidasesHemoglobinsHumansKineticsPeptide FragmentsPlasmodium falciparumProtozoan ProteinsSubstrate SpecificityJournal ArticleResearch Support, U.S. Gov't, P.H.S.

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Eva S Istvan, Daniel E Goldberg. 2004-12-01. Distal substrate interactions enhance plasmepsin activity.. https://doi.org/10.1074/jbc.m412086200

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