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Fig. 2 | BMC Bioinformatics

Fig. 2

From: Phage spanins: diversity, topological dynamics and gene convergence

Fig. 2

a: Predicted secondary structures of lambda i-spanin Rz, o-spanin Rz1 and T1 u-spanin gp11. The TMDs in Rz and gp11 are shown as crossed and hatched rectangles respectively, while the lipoylation signal sequences in Rz1 and gp11 are shown as black rectangles. Grey rectangles and black arrows indicate predicted alpha helical and beta sheet domains respectively. Coiled-coil domains CC1 and CC2 are connected through a flexible linker region. b: Cartoon representation of the topology of two-component spanin prototype from phage λ and the u-spanin from phage T1. In phage λ, i-spanin Rz is embedded to the IM by an N-terminal TMD (crossed rectangle) and has a periplasmic domain that constitutes two alpha helices (grey cylinders) connected by a linker, predicted to form coiled coils. The o-spanin Rz1 is attached to the inner leaflet of the OM via three fatty acyl chains (black lines) and has a periplasmic domain (white) predicted to be unstructured. The i- and o- spanins interact through their C-termini to form the spanin complex, linking the IM and OM though the PG meshwork. In T1, the u-spanin gp11 is attached to the inner leaflet of the OM, by the three fatty acyl chains (black lines) at the N-terminus and to the inner membrane, through the C-terminal TMD (hatched rectangle). The periplasmic domain of gp11, predicted to be mainly extended beta sheets (black arrows), connects the IM and OM through the PG meshwork. c: Cartoon representation of the model for the function of two-component (top panels) and unimolecular (bottom panels) spanins. The spanin complexes accumulate within the constraints of the PG meshwork, connecting the IM and OM (left panels). Once the PG is removed by the endolysin, these complexes are free to undergo lateral diffusion and conformational changes (middle panels). These events bring both the membranes together, leading to fusion of the IM and OM (right panels) and release of the phage progeny through the fusion pore. The model presented in the top panel has already been presented in a previous report by Rajaure et al. [10]

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