Calcium-binding sites coordination numbers

These are soluble, sarcoplasmic calcium-binding proteins found in vertebrates. Invertebrates contain different sarcoplasmic calcium-binding proteins.247 Parvalbumins are low molecular weight (10 000-12 000), acidic proteins which contain two binding sites for Ca2+. The structure of parvalbumin has been determined, and details of the calcium sites are given in Table 6. XANES studies indicate that the calcium sites are similar to those in calmodulin, but different from troponin C.244,248 The two parvalbumin sites have different coordination numbers, six and eight.249... 

The structures also revealed a Zn2+-binding site in the protein. The coordination of the zinc ion is similar to the pattern seen in certain metalloproteases (Brodersen et al 1999). Sequence comparison suggests that this zinc-binding site is present in a number of the remaining members of the S100 family (Fritz and Heizmann, 2004). The structure of S100A7, crystallised in the absence of zinc, further showed that loss of zinc resulted in a reorganisation of the adjacent empty and distorted EF-hand loop, similarly to a calcium-loaded EF-hand. 

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