Conformational Studies on C-Phycocyanin from Spirulina platensis

Abstract

Bile Pigments, Protein Interaction, Conformation, DenaturationThe chromophore-protein interactions of C-phycocyanin (C-PC) from Spirulina platensis have been studied by following the partial and complete denaturation with UV-Vis spectroscopy. From comparison with published MO calculations, an elongated conformation of the chromophore is sug gested for native C-PC, a cyclic one for denatured C-PC. By means of partial denaturation, a step wise unfolding of the protein has been demonstrated. The presence of at least two sets of spectro scopically different diromophores is suggested from the partial denaturation and low temperature experiments.Phycocyanins and phycoerythrins are photosyn thetic light harvesting pigments of blue-green, red and cryptophytan algae, which contain bile-pigment chromophores covalently bound to p ro tein s2. The absorption of the various types of these pigments cover the spectral range between about 500 and 670 nm practically completely. In spite of this spec tral variety, however, the phycobiliproteins contain with only few exceptions just two chemically distinct chromophores: the blue phycocyanobilin ( la ) and the red phycoerythrobilin (2) *• 2> 3. Uninfluenced by the protein, the free bases of the two chromola : Rj = Protein; R2 = C^Hs lb : Ri = Protein; R2 = C2H3 2: R = Protein * The terms phycocyanobilin and phycoerythrobilin are used for compounds with the molecular structure of la and 2, which are characterized by a substituted ethylgroup at C-3. For a critical discussion, see ref.2.

Chromophores in Photomorphogenesis

“…Stepwise denaturation has been observed with PC from Spirulina platensis, suggesting a distinct intermediate in the unfolding process (SCHEER and KUFER 1977). Similar intermediates may be present in the pigments isolated from T.…”

“…Unfortunately, unfolding of P r is irreversible. The process is fully reversible, however, with PC and PE and was investigated in more detail with these biliproteins by absorption, fluorescence, circular dichroism and chemical methods (SCHEER and KUFER 1977. Especially PC exhibits differences between the native and the denatured state which are very similar to those in P r -A 2 /Aj, which is roughly proportional to f 2 /fi, increases from 0.24 to 2.32 in PC and from 0.35 to 2.27 in P r .…”

Phycobilisomes and Isolated Phycobiliproteins. Effect of Glutardialdehyde and Benzoquinone on Fluorescence

“…The biphasic decrease can be due to either two consecutive reactions, or to a differential effect on the different types of the chromophores (Zickendraht-Wendeistadt et Grabowski and Gantt, 1978;Teale and Dale, 1970;Vernotte, 1971;Langer et al, 1980). Such a differential reactivity has been observed, for example, in C-PC, during denaturation (Scheer and Kufer, 1977) and The data are taken at ambient temperature (298 K) and at 77 K without and after glutardialdehyde (GA) and benzoquinone (BQ) treatment, respectively. In each case, immediately following the measurement at room temperature, the sample was cooled down to 77 K (time needed: 30min).…”

Immunochemical Characterization of Porphyridium cruentum B-Phycoerythrin: Proof of Cross-Reaction between Chromophore-Free Apoprotein and Holoprotein-Specific Antibodies

“…[33][34][35][36], for review see [37], immunological methods have been applied on a num ber of biliproteins from various organisms [10,26,27,38,39], In some cases, im munological cross-reactions have been reported; for example, antisera against C-PC of a red alga reacts with C-PC of a cyanobacterium [10], Cross-reaction between different classes of biliproteins was not observed, e.g. antibodies against B-PE do not recognice C-PC [10].…”