Selective peptidic and peptidomimetic inhibitors of Candida albicans MyristoylCoA: Protein N-myristoyltransferase: A new approach to antifungal therapy

James A. Sikorski, Balekudru Devadas, Mark E. Zupec, Sandra K. Freeman, David L. Brown, Hwang Fun Lu, Srinivasan Nagarajan, Pramod P. Mehta, Arlene C. Wade, Nandini S. Kishore, Martin L. Bryant, Daniel P. Getman, Charles A. McWherter, Jeffrey I. Gordon

Research output: Contribution to journalArticlepeer-review

55 Scopus citations

Abstract

Myristoyl CoA:protein N-myristoyltransferase (NMT) catalyzes the cotranslational covalent attachment of a rare cellular fatty acid, myristate, to the N-terminal Gly residue of a variety of eukaryotic proteins. The myristoyl moiety is often essential for expression of the biological functions for these proteins. Attachment of C14:0 alone provides barely enough hydrophobicity to allow stable association with membranes. The partitioning of N-myrisotylproteins is therefore often modulated by "switches" that function through additional covalent or noncovalent modifications. Candida albicans, the principal cause of systemic fungal infection in immunocompromised humans, contains a single NMT gene that is essential for its viability. The functional properties of the acylCoA binding site of human and C. albicans NMT are very similar. However, there are distinct differences in their peptide binding sites. An ADP ribosylauon factor (Arf) is included among the few cellular protein substrates of the fungal enzyme. Alanine scanning mutagenesis of an octapeptide derived from an N-terminal Arf sequence (GLYASKLS-NH2) disclosed that Gly1, Ser5, and Lys6 play predominant roles in binding. ALYASKLS-NH2 is an inhibitor competitive for peptide [Ki(app) = 15.3 ± 6.4 μM] and noncom- petitivefor myristoyl CoA. Remarkably, replacement of the N-terminal tetrapeptide with an 11-aminoundecanoyl group results in a competitive inhibitor (11-aminoundecanoyl-SKLS-NH2) that is ∼ 40-fold more potent [Ki(app) = 0.40 ± 0.03 μM] than the starting octapeptide. Removal of Leu-Ser from the C-terminus generates a competitive dipeptide inhibitor (11-aminoundecanoyl-SK-NH2) with a Ki(app) of 11.7 ± 0.4 μM, equivalent to that of the starting octapeptide. A derivative dipeptide inhibitor containing a C-terminal N-cyclohexylethyl lysinamide moiety has the advantage of being more potent (IC50 = 0.11 ± 0.03 μM) and resistant to digestion by cellular carboxypeptidases. Rigidifying the flexible aminoundecanoyl chain results in very potent general NMT inhibitors (IC50 = 40-50 nM). Substituting a 2-methylimidazole for the N-terminal amine and adding a benzylic α-methyl group with R stereochemistry to the rigidifying element produces even more potent inhibitors (IC50 = 20-50 nM) that are up to 500-fold selective for the fungal compared to human enzyme. A related less potent member of this series of compounds is fungistatic. Its growth inhibitory effects are associated with a reduction in cellular protein N-myristoylalion, judged using cellular Arf as a reporter. These studies establish that NMT is a new antifungal target.

Original languageEnglish
Pages (from-to)43-71
Number of pages29
JournalBiopolymers
Volume43
Issue number1
DOIs
StatePublished - 1997

Keywords

  • Antifungal therapy: Candida albicans
  • Myristoyl CoA:protein N-myristoyltransferase
  • Peptidamimetic inhibitors
  • Peptidic inhibitors

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