Copper binding affinity of the C2B domain of synaptotagmin-1 and its potential role in the nonclassical secretion of acidic fibroblast growth factor

Abstract

Fibroblast growth factor 1 (FGF1) is a heparin-binding proangiogenic protein. FGF1 lacks the conventional N-terminal signal peptide required for secretion through the endoplasmic reticulum (ER) -Golgi secretory pathway. FGF1 is released through a Cu2+ - mediated nonclassical secretion pathway. The secretion of FGF1 involves the formation of a Cu2+- mediated multiprotein release complex (MRC) including FGF1, S100A13 (a calcium-binding protein) and p40 synaptotagmin (Syt1). It is believed that binding of Cu2+ to the C2B domain is important for the release of FGF1 in to the extracellular medium. In this study, using a variety of biophysical studies, Cu2+ and lipid interactions of the C2B domain of Syt1were characterized. Isothermal titration calorimetry (ITC) experiments reveal that C2B domain binds to Cu2+ in a biphasic manner involving an initial endothermic and a subsequent exothermic phase. Fluorescence energy transfer experiments using Tb3+ show that there are two Cu2+- binding pockets on the C2B domain, and one of these is also a Ca2+- binding site. Lipid-binding studies using ITC demonstrate that the C2B domain preferentially binds to small unilamellar vesicles of phosphatidyl serine (PS). Results of the differential scanning calorimetry and limited trypsin digestion experiments suggest that C2B domain is marginally destabilized upon binding to PS vesicles. These results, for the first time, suggest that the main role of the C2B domain of Syt1 is to serve as an anchor for the FGF1 MRC on the membrane bilayer. In addition, binding of the C2B domain to the lipid bilayer is shown to significantly decrease the binding affinity of the protein to Cu2+. The study provides valuable insights on the sequence of structural events that occur in the nonclassical secretion of FGF1.

SCG5 and MITF may be novel markers of copper metabolism immunorelevance in Alzheimer’s disease

“…CCK is also important for AD hippocampal cognition, according to Liu et al 35 . SYT1 (synaptotagmin 1) is involved in neurotransmission 36 , and its C2B domain's binding affinity to lipids is significantly affected by Cu 2+37 and also affects lipid binding 38 . SYT1 is essential for the release of neurotransmitters from hippocampal neurons.…”

Annexin A2 Flop-Out Mediates the Non-Vesicular Release of DAMPs/Alarmins from C6 Glioma Cells Induced by Serum-Free Conditions

“…Biological molecules, including damage-associated molecular patterns (DAMPs)/alarmins, are extracellularly released in distinct modes via exocytosis by various mechanisms involving lysosomes (interleukin (IL)-1β, high-mobility group box 1 (HMGB1)), exosomes (galectin-3), exovesicles (galectins and transglutaminase), and transporters (fibroblast growth factor (FGF)-2) [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ]. The mechanism of stress-induced non-classical release of FGF-1 and IL-1α was initially reported by Prudovsky, Maciaq, and their colleagues [ 1 , 9 , 10 ], followed by our studies on the release of FGF-1 and prothymosin α (ProTα) [ 11 , 12 , 13 , 14 ].…”

Nanotechnology connecting copper metabolism and tumor therapy

“…[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] According to several studies, different malignant tumors have higher Cu contents than normal tissues. 34 Cu can stimulate angiogenesis, 35 which is necessary for the growth and metastasis of tumors, by activating angiogenic proteins like angiopoietin (Ang), vascular endothelial growth factor (VEGF), [36][37][38][39] fibroblast growth factor 1 (FGF1), 40 and interleukin-1 (IL-1), and promote angiogenesis. [41][42][43][44] Therefore, Cu-exhaustion-related cancer therapy emerges at the historic moment.…”