Biology subjects

Modahl, C.

Publications and source records attributed to Modahl, C..

3 recordsLinked to original sources

bioRxiv2025

Structural and functional characterisation of isolated puff adder (B. arietans) serine proteases

Serine proteases are known to play a major role in the haemotoxic actions of viper venom, but compared with those from other vipers, the serine proteases of puff adder venoms have not been extensively characterised. To address this, we isolated, identified and characterised the bioactivity of the serine proteases within the venom of the Nigerian puff adder which we had previously shown to be especially rich in this class of toxin. Two distinct groups were identified, each with different protein substrate specificities. Both had similar molecular weights of 52-62 kDa, with 4-6 N-glycans, but one group consisted of trypsin-like acidic SVSPs and the other were chymotrypsin-like basic SVSPs. Each acted differently on fibrinogen: the acidic SVSPs showed thrombin-like alpha/beta-fibrinogenase activity, whereas the basic forms were shown to be alpha-fibrinogenases. The acidic SVSPs possess gelatinase activity - a novel activity for SVSPs and the first example of an SVSP acting on proteins other than those of the haemostatic system. Analysis of the transcripts of both sets of SVSPs revealed structural details of the substrate-binding sites that supported the experimental findings. The activity and sequences of the basic SVSPs show that they are very like the alpha-fibrinogenase ML-AF of M. lebetina, which until now was considered to be a unique SVSP. Thus, this basic SVSP and the acidic SVSP with its gelatinase activity can be considered to be atypical viper serine proteases. The gelatinase activity of the acidic SVSPs was found to vary geographically and this, alongside the regional variation in the SVMP activities that we observed previous study, is discussed with reference to the potential implications on pathology of envenoming and the development of therapeutic interventions.

biochemistry↗

bioRxiv2025

Multiple orthoflaviviruses secrete sfRNA in mosquito saliva to promote transmission by inhibiting MDA5-mediated early interferon response

Numerous orthoflaviviruses transmitted through the bites of different mosquito species infect more than 500 million people annually. Skin infection at the bite site represents a critical and conserved step in transmission and a deeper understanding of this process will promote the design of broad-spectrum interventions to address diverse orthoflavivirus health threats. Here, we identify and characterize a transmission-enhancing viral factor in mosquito saliva that is shared across orthoflaviviruses. Saliva from West Nile virus-infected Culex and Zika virus-infected Aedes contains a viral non-coding RNA, subgenomic flaviviral RNA (sfRNA), within lipid vesicles distinct from virions. Higher concentration of sfRNA in infectious saliva positively correlates with infection intensity in human cells and skin explants. Early sfRNA delivery into transmission-relevant skin cell types and human skin explant demonstrate that sfRNA is responsible for the infection enhancement. Co-inoculation of sfRNA in a mouse model of transmission enhanced skin infection and worsened disease severity, supporting the role of salivary sfRNA as a transmission-enhancer. Mechanistically, salivary sfRNA attenuates early interferon response in human skin cells and skin explants by disrupting MDA5 signaling. Our results, derived from two distinct orthoflaviviruses and supported by prior studies, establish salivary sfRNA as a pan-orthoflavivirus transmission-enhancing factor driven by a conserved viral non-coding RNA.

immunology↗

bioRxiv2024

Isolation and characterisation of serine proteases and metalloproteases from the venom of African puff adders

The puff adder (Bitis arietans) is a highly venomous viper responsible for many fatalities in Africa, yet there have been few comprehensive analyses of its venom proteins, particularly of the proteases that play a key role in pathology of envenoming. To address this, we have isolated, identified and characterised the bioactivity of the venom metalloproteases of puff adders obtained from a wide range of sources. Prominent in all venoms was an SVMP PI, derived from a PII precursor. This protein existed in either of two forms: non-glycosylated (21 kDa) or glycosylated with either one (26 kDa) or two N-glycans (30 kDa). All the venoms we tested here were found to contain either one or the other form: none had both. The 21 kDa form proved to be highly potent, with alpha-, beta- and in some cases gamma-fibrinogenase activities and were very destructive towards laminin. Prothrombin and Factor X were also extensively degraded by the 21 kDa SVMP, but in neither case did this result in generation of the respective active forms of these clotting factors. In contrast, the two-glycan forms were markedly less active against all of these substrates. The one-glycan form isolated from a Kenyan venom possessed activities that was intermediate between the non- and two-glycan forms. Because of the predominance and ubiquity of these SVMPs in puff adders, and their undoubted clinical significance, we propose to name them the arilysins. The SVMP PIII content of the puff adder venoms was, atypically for African vipers, quite low. In some Kenyan venoms, however, there was an abundant SVMP PIII, with strong gelatinase activity. This protein possesses an unusual oligomeric structure, being a 140 kDa homodimer (c.f. SVMPIII-c) but without the disulphide bonds that normally hold the monomers together in this class of SVMP. This diversity in venom metalloprotease activities is discussed with reference to the potential implications on the pathology of envenomation and the development of therapeutic interventions.

biochemistry↗