Metal ion binding to parvalbumin and fulvic acids

The helix-loop-helix (EF-hand) motif is characteristic of the calcium binding protein superfamily. Molecular dynamics (MD) computations were used to study the major parvalbumin from the New England Silver Hake (SHPV-B) and the internal helix-loop-helix region (CD) functional fragment. SHPV-B contains a conserved glutamate at position 59 (the so-called gateway position) in the primary sequence, which has been shown to tune calcium binding and release. The gateway position of SHPV-B was mutated from glutamate to arginine, cysteine, serine and aspartic acid, residues which have never been found at the gateway position of any parvalbumin, but have been found at the gateway position in other EF-hand proteins including oncomodulin and calmodulin. The results of our MD simulations show that all variants are very disruptive to the calcium ion site in the whole protein. In contrast, only the arginine and cysteine mutations are disruptive in the isolated CD fragment. The serine and aspartic acid variants of the CD fragment exhibited remarkable stability during the entire MD simulation, with retention of calcium binding. Thus, there are no inherent problems for calcium binding associated with the sequence of the CD segment that precludes the incorporation of serine or aspartic acid at the gateway position of parvalbumin. The binding problems observed in the whole protein are most likely related to the unique interaction between the paired EF-hands.; MD and experimental studies were also used to examine the conformational changes in SHPV-B upon calcium removal. The CD and EF helices undergo a reorientation to an approximately parallel orientation (from the perpendicular orientation in the x-ray structure) in the isolated CD and CDEF fragments of SHPV-B, but not in the whole protein. Metal ion and herbicide binding to Suwannee River Fulvic Acid (SRFA) was probed using fluorescence and infrared spectroscopy. Fulvic acid complexation to metals and organics can increase their bio-availability. In contrast to SRFA binding to most metals examined, fluorescence enhancement was observed upon aluminum binding and fluorescence quenching was observed upon palladium binding. The unique fluorescence responses likely arises from the differing covalent and ionic binding character of the metals. The data indicates that aluminum interacts with both salicylic acid and phthalic acid moieties in SRFA. The data also suggests that herbicides can bind to fulvic acids via metal ion bridges.