Insulin-regulated aminopeptidase: analysis of peptide substrate and inhibitor binding to the catalytic domain.
Peptide inhibitors of insulin-regulated aminopeptidase (IRAP) accelerate spatial learning and facilitate memory retention and retrieval by binding competitively to the catalytic site of the enzyme and inhibiting its catalytic activity. IRAP belongs to the M1 family of Zn2+-dependent aminopeptidases characterized by a catalytic domain that contains two conserved motifs, the HEXXH(X)18E Zn2+-binding motif and the GXMEN exopeptidase motif. To elucidate the role of GXMEN in binding peptide substrates and competitive inhibitors, site-directed mutagenesis was performed on the motif. Non-conserved mutations of residues G428, A429 and N432 resulted in mutant enzymes with altered catalytic activity, as well as divergent changes in kinetic properties towards the synthetic substrate leucine beta-naphthylamide. The affinities of the IRAP inhibitors angiotensin IV, Nle1-angiotensin IV, and LVV-hemorphin-7 were selectively decreased. Substrate degradation studies using the in vitro substrates vasopressin and Leu-enkephalin showed that replacement of G428 by either D, E or Q selectively abolished the catalysis of Leu-enkephalin, while [A429G]IRAP and [N432A]IRAP mutants were incapable of cleaving both substrates. These mutational studies indicate that G428, A429 and N432 are important for binding of both peptide substrates and inhibitors, and confirm previous results demonstrating that peptide IRAP inhibitors competitively bind to its catalytic site.
Ye
Siying
S
Howard Florey Institute, University of Melbourne, Parkville, Victoria 3010, Australia.
Chai
Siew Yeen
SY
Lew
Rebecca A
RA
Albiston
Anthony L
AL
D000804:Angiotensin II / Q000031:analogs & derivatives / Q000378:metabolism; D001127:Arginine Vasopressin / Q000378:metabolism; D020134:Catalytic Domain / Q000502:physiology*; D010122:Cystinyl Aminopeptidase / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D004743:Enkephalin, Leucine / Q000378:metabolism; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D009154:Mutation; D010446:Peptide Fragments / Q000378:metabolism
D006454:Hemoglobins; D010446:Peptide Fragments; D000804:Angiotensin II; D001127:Arginine Vasopressin; C012877:angiotensin II, des-Asp(1)-des-Arg(2)-Ile(5)-; D004743:Enkephalin, Leucine; C074309:LVV-hemorphin-7; D010122:Cystinyl Aminopeptidase; C105964:leucyl-cystinyl aminopeptidase