Biology subjects

Giglio, M. L.

Publications and source records attributed to Giglio, M. L..

2 recordsLinked to original sources

bioRxiv2025

Conkazal-M1 from the MKAVA family of conotoxins - a dual-function protease inhibitor and neuroactive peptide

Marine cone snails produce a diverse array of bioactive peptides, known as conotoxins, in their venom. Given their high target potency and specificity, conotoxins are attractive compounds for the development of precision research tools and pharmacological agents. Here, we provide the first experimental characterization of a conotoxin from the MKAVA superfamily, conkazal-M1, from Conus magus. Using NMR spectroscopy, we show that conkazal-M1 adopts a fold characteristic of the Kazal-type protease inhibitor family, featuring a Glu residue at the inhibitory P1 position. Recombinantly expressed conkazal-M1 inhibits the proteolytic activity of Subtilisin A with an apparent Ki of 1.1 M. In addition, conkazal-M1 partially inhibits calcium transients in mouse sensory neurons, suggesting a potential role in modulating ion-channel activity, as seen for many other toxins. The dual function of conkazal-M1 in protease inhibition and neuroactivity is analogous to the dual function of several toxins harboring a Kunitz-type fold. The well-conserved sequence of the MKAVAs indicates an evolutionary trajectory in which these proteins face an adaptive conflict, where mutations that enhance one activity compromise the other. Collectively, this work provides new structural and functional insights into a previously uncharacterized toxin superfamily in cone snails, illustrates how structural scaffolds can be repurposed for functions that diverge from the original while retaining their overall structure, and expands our understanding of the toxin arsenal available to venomous animals.

biochemistry↗

bioRxiv2019

Exaptation of two ancient immune proteins into a new dimeric pore-forming toxin in snails

The Membrane Attack Complex-Perforin (MACPF) family is ubiquitously found in all kingdoms. They have diverse cellular roles but MACPF but pore-forming toxic function are very rare in animals. Here we present the structure of PmPV2, a MACPF toxin from the poisonous apple snail eggs, that can affect the digestive and nervous systems of potential predators. We report the three-dimensional structure of PmPV2, at 15 [A] resolution determined by negative stain electron microscopy (NS-EM) and its solution structure by small angle X-ray scattering (SAXS). We found that PV2s differ from nearly all MACPFs in two respects: it is a dimer in solution and protomers combine two immune proteins into an AB toxin. MACPF chain is linked by a single disulfide bond to a tachylectin chain, and two heterodimers are arranged head-to-tail by non-covalent forces in the native protein. MACPF domain is fused with a putative new Ct-accessory domain exclusive to invertebrates. Tachylectin is a six-bladed {beta}-propeller, similar to animal tectonins. We experimentally validated the predicted functions of both subunits and demonstrated for the first time that PV2s are true pore-forming toxins. The tachylectin ..B.. delivery subunit would bind to target membranes, and then its MACPF ..A.. toxic subunit disrupt lipid bilayers forming large pores altering the plasma membrane conductance. These results indicate that PV2s toxicity evolved by linking two immune proteins where their combined preexisting functions give rise to a new toxic entity with a novel role in defense against predation. This structure is an unparalleled example of protein exaptation.

biochemistry↗