Minicollagen cysteine-rich domains encode distinct modes of polymerization to form stable nematocyst capsules

Abstract

The stinging capsules of cnidarians, nematocysts, function as harpoon-like organelles with unusual biomechanical properties. The nanosecond discharge of the nematocyst requires a dense protein network of the capsule structure withstanding an internal pressure of up to 150 bar. Main components of the capsule are short collagens, so-called minicollagens, that form extended polymers by disulfide reshuffling of their cysteine-rich domains (CRDs). Although CRDs have identical cysteine patterns, they exhibit different structures and disulfide connectivity at minicollagen N and C-termini. We show that the structurally divergent CRDs have different cross-linking potentials in vitro and in vivo. While the C-CRD can participate in several simultaneous intermolecular disulfides and functions as a cystine knot after minicollagen synthesis, the N-CRD is monovalent. Our combined experimental and computational analyses reveal the cysteines in the C-CRD fold to exhibit a higher structural propensity for disulfide bonding and a faster kinetics of polymerization. During nematocyst maturation, the highly reactive C-CRD is instrumental in efficient cross-linking of minicollagens to form pressure resistant capsules. The higher ratio of C-CRD folding types evidenced in the medusozoan lineage might have fostered the evolution of novel, predatory nematocyst types in cnidarians with a free-swimming medusa stage.

A genome wide survey reveals multiple nematocyst-specific genes in Myxozoa

“…Interestingly, CRDs also characterize minicollagens and other important structural nematocyst proteins [ 11 , 31 – 33 ]. Specifically, the CRDs of minicollagens are known to polymerize to form the basic scaffold of the nematocyst capsule [ 32 , 34 , 35 ]. A signal peptide was identified for all sequences that were not truncated at their 5’end.…”

Disulfide Crosslinked Hydrogels Made From the Hydra Stinging Cell Protein, Minicollagen-1

“…The CRDs are present in numerous proteins involved in nematocyst biosynthesis and function (Ozbek et al, 2009;Balasubramanian et al, 2012). Recently, it was shown that the CRDs facilitate multimerization of proteins through direct interaction with each other, and that certain CRD sequences enable a higher interaction valency than others (Tursch et al, 2016). The dynamic nature of the CRD disulfide bonds has been demonstrated in the creation of re-codable surfaces where surface chemistry of a substrate can be written and re-written using the reversible nature of the CRD disulfide bonds (Gegenhuber et al, 2017).…”

“…The CRDs are proposed to perform two functions in the creation of nematocyst structures. First, they function as multimerization domains that control organization and self-assembly of higher order protein complexes (Meier et al, 2007;Tursch et al, 2016). Second, they contain stored intrachain disulfide bonds that are mobilized at the right time to create interchain crosslinks that stabilize the protein complexes (Meier et al, 2007;Beckmann et al, 2015).…”

The Sialic Acid-Dependent Nematocyst Discharge Process in Relation to Its Physical-Chemical Properties Is a Role Model for Nanomedical Diagnostic and Therapeutic Tools

“…Therefore, the structural elements responsible for their distinct structures were analyzed to gain possible information about the mechanisms of mini-collagen disulfide rearrangement in their assembly into polymeric fibers. With better information on this process, mini-collagens containing functional domains of type I and IV collagens could be used for the preparation of mechanically highly resistant frameworks for cell adhesion and thus constitute promising innovative biomaterials [34]. However, their architecture is also of interest when nematocyts in various intact nematocytes are tested concerning its diagnostic feasibility when coming into contact with sialic acid coated surfaces.…”