Vance, Steven J.
The relationship between structure and function in natural surfactant proteins.
PhD thesis, University of Glasgow.
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Surfactant activity is a property more commonly associated with small molecules than biological macromolecules. However, the significant advantages of improved biodegradability and biocompatibility that could be presented by natural surfactant proteins has elevated interest in a group of only a few proteins where intrinsic surfactant activity appears to be the primary function. Two examples of this group, ranaspumin-2 (Rsn-2) from the foam nests of the tungara frog and latherin, the surface active protein component of horse sweat, appear to be different from other surfactant proteins in the form of their activity. However, the exact molecular basis of this activity is poorly understood. This thesis describes work to rationalise surface activity and related properties in these unusual proteins.
The properties of Rsn-2 and latherin including surface activity, interaction with lipid membranes and behaviour in solution were investigated to provide further insight into the characteristics that distinguish the surfactant proteins from both conventional surfactants and other proteins. A second protein component of the foam nests, ranaspumin-1 (Rsn-1), of previously unknown function was also found to be highly surface active and is proposed to function in a similar manner to Rsn-2.
A model whereby Rsn-2 functions via a clamshell-like opening was tested through a combination of specialised NMR techniques and site-directed mutagenesis. The results identified features associated with surfactant activity, all of which were consistent with the model. The potential of Rsn-2 as a recombinant fusion partner for the production of functional surfactants or foams was proven by construction of a fluorescent conjugate.
Solution state NMR was used to determine the structure of latherin. Information on the dynamic processes taking place in the molecule were derived by analysis of NMR relaxation data. The structure revealed is a super roll fold, similar to a single domain of the BPI-like proteins. A model is proposed whereby latherin recognises the air-water interface via three dynamic, hydrophobic loops at one end of its long cylindrical structure and then unfolds to expose its hydrophobic core at the air-water interface.
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