S3 to S3' subsite specificity of recombinant human cathepsin K and development of selective internally quenched fluorescent substrates

• Published in: Biochemical journal 2003-08, Vol.373 (Pt 3), p.981-986
• Main Authors: Alves, Marcio F M, Puzer, Luciano, Cotrin, Simone S, Juliano, Maria Aparecida, Juliano, Luiz, Brömme, Dieter, Carmona, Adriana K
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Bradykinin - metabolism; Cathepsin K; Cathepsins - metabolism; Fluorescent Dyes - metabolism; Humans; Recombinant Proteins - metabolism; Substrate Specificity
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/BJ20030438

We have systematically examined the S3 to S3' subsite substrate specificity requirements of cathepsin K using internally quenched fluorescent peptides derived from the lead sequence Abz-KLRFSKQ-EDDnp [where Abz is o -aminobenzoic acid and EDDnp is N -(2,4-dinitrophenyl)ethylenediamine]. We assayed six series of peptides, in which each position except Gln was substituted with various natural amino acids. The results indicated that the S3-S1 subsite requirements are more restricted than those of S1'-S3'. Cathepsin K preferentially accommodates hydrophobic amino acids with aliphatic side chains (Leu, Ile and Val) in the S2 site. Modifications at P1 residues also have a large influence on cathepsin K activity. Positively charged residues (Arg and Lys) represent the best accepted amino acids in this position, although a particular preference for Gly was found as well. Subsite S3 accepted preferentially basic amino acids such as Lys and Arg. A broad range of amino acids was accommodated in the remaining subsites. We further explored the acceptance of a Pro residue in the P2 position by cathepsin K in order to develop specific substrates for the enzyme. Two series of peptides with the general sequences Abz-KXPGSKQ-EDDnp and Abz-KPXGSKQ-EDDnp (where X denotes the position of the amino acid that is altered) were synthesized. The substrates Abz-KPRGSKQ-EDDnp and Abz-KKPGSKQ-EDDnp were cleaved by cathepsin K at the Arg-Gly and Gly-Ser bonds respectively, and have been shown to be specific for cathepsin K when compared with other lysosomal cysteine proteases such as cathepsins L and B and with the aspartyl protease cathepsin D.