Dynamical Oligomerisation of Histidine Rich Intrinsically Disordered Proteins Is Regulated through Zinc-Histidine Interactions

Abstract

Intrinsically disordered proteins (IDPs) can form functional oligomers and in some cases, insoluble disease related aggregates. It is therefore vital to understand processes and mechanisms that control pathway distribution. Divalent cations including Zn2+ can initiate IDP oligomerisation through the interaction with histidine residues but the mechanisms of doing so are far from understood. Here we apply a multi-disciplinary approach using small angle X-ray scattering, nuclear magnetic resonance spectroscopy, calorimetry and computations to show that that saliva protein Histatin 5 forms highly dynamic oligomers in the presence of Zn2+. The process is critically dependent upon interaction between Zn2+ ions and distinct histidine rich binding motifs which allows for thermodynamic switching between states. We propose a molecular mechanism of oligomerisation, which may be generally applicable to other histidine rich IDPs. Finally, as Histatin 5 is an important saliva component, we suggest that Zn2+ induced oligomerisation may be crucial for maintaining saliva homeostasis.

Zinc Binding by Histatin 5 Promotes Fungicidal Membrane Disruption in C. albicans and C. glabrata

“…Hst 5 is comprised of 24 amino acid residues with multiple overlapping metal binding motifs including a Cu 2+ binding ATCUN motif [ 12 ] and two discrete Zn 2+ binding motifs including a canonical HExxH motif and another Zn 2+ -affinity sequence closer to the N-terminus, (H)AKRHH [ 14 ]. ( Figure 1 ).…”

“…The full mechanism of action remains unclear, but multiple cellular effects are known, including efflux of small molecules like potassium, magnesium [ 5 ], ATP [ 6 ], ROS generation [ 7 ], and cell cycle arrest [ 8 ]. At the same time, it was discovered that Hst 5 binds to multiple divalent cations including copper and zinc [ 9 ], potentially with physiological relevance [ 10 ], though the function of this capability is still poorly understood [ 11 , 12 , 13 , 14 , 15 , 16 ].…”

“…The effects of Zn 2+ binding on the conformation, oligomerization state, and membrane interactions of the Hst 5 peptide have been described [ 11 , 14 , 15 ], but this has also raised questions about the practical application of Zn 2+ to alter or improve fungicidal activity. Though there are studies on the effect of both copper [ 12 ] and iron [ 16 ] on Hst 5 killing activity, comparatively little is known about the direct effect of Zn 2+ on Hst 5 efficacy or the mechanism involved.…”

“…Hst 5 is capable of catalyzing vesicle fusion in the presence of Zn 2+ [ 10 ], indicating direct binding with membrane phospholipids and the ability to affect membrane structure. Importantly, Zn 2+ binding stabilizes Hst 5 in bioactive conformations [ 11 ] and also promotes dimerization [ 14 ]. Peptide dimerization and aggregation have a complex relationship with AMP activity [ 32 , 33 ] but are highly potentiating for some pore-forming peptides [ 34 , 35 , 36 ], and pre-assembly of oligomeric peptide structures can speed up pore formation [ 34 , 37 , 38 ].…”

Interactions by Disorder – A Matter of Context

“…Chain compaction may further be affected by metal ions, as observed for Zn 2+ binding to ProTα, and to histatin, a small peptide of the mouth, here promoting formation of higher order structures (Cragnell et al, 2019). For both IDPs, these are Zn 2+ -specific effects (Yi et al, 2007;Cragnell et al, 2019).…”