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Altering ionic strength and pH changes the folding pathway of lysozyme Sunita Kulkarni, Department of Biochemistry and Molecular Biology, University of Leeds Woodhouse Lane, Leeds West Yorkshire, LS2. 9JT. UK Hen egg white lysozyme has been widely used as a model system for folding studies as it is small, has a well characterised structure, and exhibits reversible folding over a measurable time scale. A similar multipronged biophysical approach as that used for elucidating the protein folding pathway of lysozyme at pH 5.2 and 20'C (Radford and Dobson, 1995) has been employed to analyse the pathway under physiological conditions. In summary, at pH 5.2, hydrophobic collapse occurs within 10ms, followed by the formation of stable a-helical structure after a further 50ms. Finally on a 300ms time scale, the native state of the enzyme forms with correct a and b domains. 75% of lysozyme molecules are thought to follow this pathway, but the remaining 25% may undergo a faster folding mechanism with a rate on a 100ms time scale to get to the native state. We are dissecting the kinetic and thermodynamic barriers thought to be responsible for the generation of the parallel pathways described above. We show here, that pH and ionic strength are important factors in the alteration of the folding mechanism from that observed at pH 5.2, leading to changes in the rate limiting step of folding, and to a sequential single pathway.The ways in which electrostatics, ionisation and hydrophobic effects may influence the early stages of protein folding, leading to routing along 'folding funnels' to the native state are considered. ## Back to the list of abstracts