Retina, calcium-binding proteins

Palczewski, K., Polans, A.S., Baehr, W., and Ames, J.B. (2000). Calcium binding proteins in the retina Structure, function, and the etiology of human visual diseases. BioEssays 22 337-350. 

Purification And Characterization Of Calcium-Binding Proteins From Retina... 

Figure 1. Flow Diagram for the Purification of Calcium-binding Proteins from Retina.

Calbindin D-28K is an example of a calcium-binding protein of the EF hand family that is not enriched through its calcium-dependent binding to phenyl-Sepharose. Instead, it can be readily purified by binding to DEAE-Sepharose in low calcium and eluted by increased calcium (Figure 2, lane h). Our studies demonstrate that calbindin D-28K is expressed in peripheral and perifoveal cone cells of the human retina but not in parafoveal or foveal cones, and this pattern of expression parallels the degeneration of photoreceptor cells seen in some humans with rod-cone dystrophies. 

A developmentally regulated polypeptide (PEP-19), that is a presumptive neuron-specific calcium binding protein, was identified in adult and neonatal rat cerebellum and its amino acid sequence was determined (Ziai et al., 1986). PEP-19-like immunoreactivity is expressed by Purkinje cells and by the cartwheel cells of the dorsal cochlear nucleus of the mouse (Mugnaini et al., 1987). Berrebi et al. (1991) drew attention to the expression of PEP-19, CaBP and other Purkinje cell markers (cerebellin, L7 see below) by bipolar cells and other neurons of the retina. 

A variety of guanine nucleotide binding proteins (G-proteins) involved with the regulation of adenylate cyclase activity and transducin in the retina (Section 2.3.1) are substrates for ADP-ribosylation. Cholera toxin and E. coli enterotoxin LT ADP-ribosylate, and hence activate, the stimulatory G-protein of adenylate cyclase, whereas pertussis toxin ADP-ribosylates, and inactivates the inhibitory G-protein of adenylate cyclase. The result of ADP-ribosylation by either mechanism is increased adenylate cyclase activity, and an increase in intracellular cAMP and the opening of membrane calcium channels. Again, there are endogenous ADP-ribosyltransferases that modify the same G-proteins, but in a controlled manner (Moss et al., 1997, 1999). 

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