Table IV.

Location of C_R, if present, in each Prx subfamily

	Canonical location of CR	Subfamily members with CR in canonical location (%)	Subfamily members with only 1 Cys in sequence (%)a	Subfamily members with alternative locations for CR (location, %)	Uncertainb (%)
BCP/PrxQ	Helix α2c (CPXXXXCR)	54	13	Helix α3 7	26
AhpC/Prx1	C-terminusd	99.1	0.4	-	0.5
Prx6	No CR	-	40	C-terminus 1.6 Helix α3 0.8	57
Prx5	Helix α5	17	14	-	69e
Tpx	Helix α3f	96.4	1.0	-	2.6
AhpEg	No CR	-	28	Helix α2 56	16

^aIf no C_R is present, the resolving thiol must come from another protein or a small molecule thiol like glutathione.

^bThese sequences contain more than one Cys, however the other Cys are not in a location shown to serve as a C_R. Many of these proteins are expected to function as 1-Cys Prxs, but this cannot be proven without experimental verification.

^cStructural designations come from Hall et al 2010¹⁶.

^dThe C_R for the AhpC/Prx1 subfamily is found near the C-terminus where it forms a disulfide bond across the B-interface with the C_P on its partner subunit. Mycobacterium tuberculosis AhpC contains a third Cys that is present two residues after the canonical C_R that may in some cases act as a replacement for the C_R ⁷⁸. While 6.7% of the AhpC/Prx1 proteins contain the C_RXC motif, 2.2% contained only the second Cys, providing support for its ability to serve a functional role.

^eThis category includes the 16% of Prx5 subfamily members that are fused to a Grx domain.

^fThe C_R in the Tpx subfamily is located immediately following the highly conserved Trp used as a key residue to create the functional site signatures – Cys92 in Fig 3E.

^gThe canonical AhpE from M. tuberculosis has no C_R, but a majority of the subfamily members identified here have a putative C_R five residues after the C_P, similar to the BCP/PrxQ subfamily.