Initial rates^a of peptides cleavage by cysteine cathepsin proteases.

Peptide	Sequence	Cts L	Cts V	Cts K	Cts S	Cts B
K3A	μHLFKAAAμ	0.181 ± 0.003	0.511 ± 0.025	0.689 ± 0.045	0.110 ± 0.002	1.921 ± 0.206
KS3A	μHLFKSAAAμ	0.014 ± 0.000	0.002 ± 0.000b	0.002 ± 0.000b	0.000 ± 0.000b	3.643 ± 0.153
R3A	μHLFRAAAμ	0.112 ± 0.003	0.363 ± 0.014	0.564 ± 0.024	0.189 ± 0.004	2.747 ± 0.265
RS3A	μHLFRSAAAμ	0.023 ± 0.000	0.002 ± 0.000b	0.001 ± 0.000b	0.002 ± 0.000b	3.968 ± 0.209
R1A	μHLFRAμ	0.125 ± 0.003	0.553 ± 0.021	0.402 ± 0.021	0.053 ± 0.000	1.034 ± 0.074
RS1A	μHLFRSAμ	0.000 ± 0.000b	0.005 ± 0.000b	0.000 ± 0.000b	0.000 ± 0.000b	0.003 ± 0.000b

^aAll rates are reported in μM min⁻¹. Rates and standard errors are calculated by fitting to linear regression function in Prism 8.

^bMALDI MS and HPLC confirmed essentially no cleavage with these peptides. Details are reported in the ESI.