TABLE 4.

Comparison of HIV-1 PR and FIV PR substrate selectivities: cleavage of the peptide series based on the peptide Ac-KSGVFVVNGLVK-NH₂^a

Peptide		PRb		HIV-1 PR/ FIV PRc
Cleavage	Sequenced	FIV	HIV-1
1	KSGVF↓VVNGLVK	++	++	0.85
2	KSFVF↓VVNGLVK	++	++	0.74
3	KSGIF↓VVNGLVK	++++	++++
4	KSGNF↓VVN ∗ GLVK	−	+++	>100
5	KSGVN↓VVNGK	−	−
5b	KSRVN↓VVNGK	+	−	<1/50
6	KSGVQ↓VVNGK	−	−
6b	KSRVQ↓VVNGK	+	−	<1/15
7	KSGVF↓HVN ∗ GLVK	++	++++
7b	KSGVF↓HVNGK	++++	++++
8	KSGVF↓SVNGLVK	++++	+	<1/3.5
9	KSGVF↓QVN ∗ GLVK	++	++
10	KSGVF↓VNNGLVK	−	−
11	KSGVF↓VENGLVK	+	++++	>10
12	KSGVF↓VQNGLVK	−	++++	>74
13	KSGVF↓VVQGLVK	++++	++++
14	KSGVF↓VVTGLVK	++++	++++

^aPeptides were subjected to digestion with 78 nM HIV-1 PR and 156 nM FIV PR for 4 h at pH 6.7 in 0.2 M NaCl. All peptides were acetylated at the N terminus, and amides were acetylated at the C terminus. All cleavages were run on 100 μM substrate except cleavages 5, 6, and 7, which were cleaved at 500 μM. 

^b++++, 100% cleavage of substrate; +++, >70% cleavage of substrate but <100% cleavage; ++, <70% cleavage but >30% cleavage; +, <30% cleavage; −, no detection of cleavage by HPLC. Quantitation based on cleavage at the arrowed site only. 

^cThe ratio of concentration of cleavage product for HIV-1 PR cleavage to the concentration of cleavage product for FIV PR cleavage. 

^dThe arrow indicates the scissile bond which was used for the determination of cleavage results. The peptide in italics was the model for identifying differences in specificity between HIV-1 PR and FIV PR. The underlined amino acid is the single amino acid change from the starting peptide sequence (in italics). The asterisk indicates a cleavage at an alternate site by FIV PR. The peptide Ac-KSGNFVVNGK-NH₂ (peptide 5) was incubated with FIV PR for 5 h without cleavage.