8.A.201.  The PacL1 Chaparone Protein (PacL1) Family 

Heavy metal cation-transporting P-type ATPase, CtpC; MtaA; Rv3270; FUPA32.2 (718 aas with at least 8 TMSs in a 4 + 2 + 2 TMS arrangement). However, there may be additional TMSs. It mediates resistance to zinc poisoning. Boudehen et al. 2022 showed that zinc resistance also depends on a chaperone-like protein, PacL1 (Rv3269). PacL1 contains an N-terminal TMS, a cytoplasmic region with glutamine/alanine repeats and a C-terminal metal-binding motif (MBM). PacL1 binds Zn²⁺, but the MBM is required only at high zinc concentrations. PacL1 co-localizes with CtpC, a heavy metal cation-transporting P-type ATPase, in dynamic foci in the mycobacterial plasma membrane, and the two proteins form high molecular weight complexes. Foci formation does not require flotillin or the PacL1 MBM. However, deletion of the PacL1 Glu/Ala repeats leads to loss of CtpC and sensitivity to zinc. Genes pacL1 and ctpC appear to be in the same operon, and homologous gene pairs are found in the genomes of other bacteria. PacL1 colocalizes and functions redundantly with other PacL orthologs in M. tuberculosis. Thus, PacL proteins may act as scaffolds that assemble P-ATPase-containing metal efflux platforms, mediating bacterial resistance to metal poisoning (Boudehen et al. 2022).