Cu + -ATPases play a key role in bacterial Cu + homeostasis by participating in Cu + detoxification and cuproprotein assembly. Characterization of Archaeoglobus fulgidus CopA, a model protein within the subfamily of P 1B-1 type ATPases, has provided structural and mechanistic details on this group of transporters. Atomic resolution structures of cytoplasmic regulatory metal binding domains (MBDs) and catalytic actuator, phosphorylation, and nucleotide binding domains are available. These, in combination with whole protein structures resulting from cryo-electron microscopy analyses, have enabled the initial modeling of these transporters. Invariant residues in helixes 6, 7 and 8 form two transmembrane metal binding sites (TM-MBSs). These bind Cu + with high affinity in a trigonal planar geometry. The cytoplasmic Cu + chaperone CopZ transfers the metal directly to the TM-MBSs; however, loading both of the TM-MBSs requires binding of nucleotides to the enzyme. In agreement with the classical transport mechanism of P-type ATPases, occupancy of both transmembrane sites by cytoplasmic Cu + is a requirement for enzyme phosphorylation and subsequent transport into the periplasmic or extracellular milieus. Recent transport studies have shown that all Cu + -ATPases drive cytoplasmic Cu + efflux, albeit with quite different transport rates in tune with their various physiological roles. Archetypical Cu + -efflux pumps responsible for Cu + tolerance, like the Escherichia coli CopA, have turnover rates ten times higher than those involved in cuproprotein assembly (or alternative functions). This explains the incapability of the latter group to significantly contribute to the metal efflux required for survival in high copper environments.

Yariv reagents are glycosylated triphenylazo dyes that bind to arabinogalactan proteins (AGPs), proteoglycans found in plant cell walls that are integral for plant growth and development. Yariv reagents are widely utilized as imaging, purification, and quantification tools for AGPs and represent the only small molecule probe for interrogating AGP function. The ability of Yariv reagents to bind to AGPs is dependent on the structure of the terminal glycoside on the dye. The reason for this selectivity has not been understood until the present work. Using circular dichroism spectroscopy, we show that the Yariv reagents form supramolecular aggregates with helical chirality. More significantly, the ability of the Yariv reagent to bind AGPs is correlated with this helical chirality. This finding paves the way towards developing a more detailed understanding of the nature of the Yariv‐AGP complex, and the design of AGP‐binding reagents with higher affinities and selectivities.

Yariv reagents are glycosylated triphenylazo dyes, some of which bind to the polysaccharide component of arabinogalactan proteins (AGPs), proteoglycans found in plant cell walls. However, the exact reason for the selectivity in the presence/absence of AGP binding ability among Yarivs remains unknown. The Yariv reagents are known to form supramolecular aggregates in solution. We use circular dichroism to show that the Yariv reagent aggregates possess helical chirality, and the AGP binding ability of the Yariv reagents is correlated to its helical chirality.

The Yariv reagents are a class of tris‐azo dyes, some of which stain and precipitate arabinogalactan proteins (AGPs), plant cell wall proteoglycans. These dyes form supramolecular aggregates in solution. In this study, CD spectroscopy revealed that the aggregates exhibit helical chirality. Only those aggregates with right‐handed helicity have a fertile interaction with AGP, while those with left‐handed helicity do not bind. Artwork credit: D. Caianiello and M. Bohne. More information can be found in the Research Article by A. Basu et al.