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Book of Abstracts: Albany 2011

category image Albany 2011
Conversation 17
June 14-18 2011
©Adenine Press (2010)

Origins of the Mechanical Stability of the C2 Domains in Human Synaptotagmin 1

Synaptotagmin 1 (Syt1) induces the buckling of plasma membrane during neurotransmitter release at the synapse (1). Therefore, elucidating the mechanical properties of Syt1 is essential for understanding its biological function in synaptic response. Syt1 contains two homologous cytoplasmic domains, C2A and C2B. We employed a self-organized polymer (SOP) model of a protein chain (2) to carry out molecular simulations, implemented on a CPU and on a GPU (Graphics Processing Unit) (3), using experimental pulling speeds. The forced unfolding of isolated C2A and C2B domains occurs under comparable forces starting from their C-terminal ends, but according to different pathways. Our results for the behavior of the C2A domain correlate very well with dynamic spectroscopy experimental studies (4,5), but no direct measurements of the mechanical behavior of the isolated C2B domain exist to date. Thus, to confirm the presence of the pathways generated with the SOP model, we also carried out implicit solvent model simulations. Atomic force microscopy (AFM) experiments found an increase in the critical unfolding force of C2B when joined with C2A in the Syt1 molecule (4), which was proposed to result from the contribution of the C2A-C2B interface. However, our simulations reveal that the presence of an intact interface does not lead to the unfolding of Syt1 according to the AFM experiments. In contrast, we discovered that the presence of linkers used in the experimental set-up plays a crucial role in the behavior of this synaptic protein complex and, their inclusion in simulations as well leads to data that fully matches the experiments. Interestingly, we found that the stabilization effect of the linker on the C2B domain alters not only the critical force, but also the unfolding pathways of both C2 domains. Our findings provide insights into the relative conformation variability of the C2 domains and the origins of stability of the Syt1 protein.



References
  1. S. Martens, M.M. Kozlov and H.T. McMahon. Science 316, 1205-1208 (2007).
  2. C. Hyeon, R. I. Dima and D. Thirumalai. Structure 14, 1633-1645 (2006).
  3. A. Zhmurov, R. I. Dima, Y. Kholodov and V. Barsegov. Proteins 78, 2984-2999 (2010).
  4. K.L. Fuson, L. Ma, R.B. Sutton and A.F. Oberhauser. Biophys. J 96, 1083-1090 (2009).
  5. M. Carrion-Vazquez, P.E. Marszalek, A.F. Oberhauser and J.M. Fernandez. PNAS 96, 11288-11292 (1999).

Li Duan 1
Artem Zhmurov2
Valeri Barsegov2
Ruxandra I. Dima1

1Department of Chemistry
University of Cincinnati
Cincinnati, OH 45221
2Department of Chemistry
University of Massachusetts
Lowell Lowell, MA 01854

Ph: (513) 556-9687
Fx: (513) 556-9687

duanli@mail.uc.edu