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Biliprotein maturation: the chromophore attachment.

Scheer H, Zhao KH - Mol. Microbiol. (2008)

Bottom Line: The discovery of new activities for the latter lyases, and of new types of lyases, have reinvigorated research activities in the subject.So far, work has mainly concentrated on cyanobacterial phycobiliproteins.Methodological advances in the process, however, as well as the finding of often large numbers of homologues, opens new possibilities for research on the subsequent assembly/disassembly of the phycobilisome in cyanobacteria and red algae, on the assembly and organization of the cryptophyte light-harvesting system, on applications in basic research such as protein folding, and on the use of phycobiliproteins for labelling.

View Article: PubMed Central - PubMed

Affiliation: Department Biologie I, Universität München, Menzinger Strasse 67, D-80638 München, Germany.

ABSTRACT
Biliproteins are a widespread group of brilliantly coloured photoreceptors characterized by linear tetrapyrrolic chromophores, bilins, which are covalently bound to the apoproteins via relatively stable thioether bonds. Covalent binding stabilizes the chromoproteins and is mandatory for phycobilisome assembly; and, it is also important in biliprotein applications such as fluorescence labelling. Covalent binding has, on the other hand, also considerably hindered biliprotein research because autocatalytic chromophore additions are rare, and information on enzymatic addition by lyases was limited to a single example, an EF-type lyase attaching phycocyanobilin to cysteine-alpha84 of C-phycocyanin. The discovery of new activities for the latter lyases, and of new types of lyases, have reinvigorated research activities in the subject. So far, work has mainly concentrated on cyanobacterial phycobiliproteins. Methodological advances in the process, however, as well as the finding of often large numbers of homologues, opens new possibilities for research on the subsequent assembly/disassembly of the phycobilisome in cyanobacteria and red algae, on the assembly and organization of the cryptophyte light-harvesting system, on applications in basic research such as protein folding, and on the use of phycobiliproteins for labelling.

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Post-translational modifications of biliproteins. Tetrapyrrole binding cysteines (consensus numbering2) with chromophores indicated in their approximate colours of the native chromoproteins (PCB in blue, PVB in purple, PEB in red, PUB in orange, MBV in green, BV in blue-green and PΦB in dark green): alternative chromophores to certain binding sites are indicated in brackets. Arrows pointing to tetrapyrrole binding sites represent identified lyases, with solid arrows indicating S-type lyases, dotted arrows T-type lyases and the dashed arrow E/F-type lyases. Boxed site numbers indicate correct autocatalytic binding, dotted boxes unclear situations. Vertical knobs indicate (partial) methylation at Asn-β72. Another PE, termed PE III, is not shown here. It has been identified in a high-light Prochlorococcus marinus, it carries only a single chromophore on the α-subunit, and none on the β-subunit (Hess et al., 1996). a, plant and most cyanobacterial phytochromes; b, bacterial, fungal and several cyanobacterial phytochromes; c, PE 545; d, only in red-algal b- (and possibly B-) PE. For biliprotein nomenclature, see Sidler (1994), Schluchter and Bryant (2002), and, alternatively (MacColl, 1998).
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fig01: Post-translational modifications of biliproteins. Tetrapyrrole binding cysteines (consensus numbering2) with chromophores indicated in their approximate colours of the native chromoproteins (PCB in blue, PVB in purple, PEB in red, PUB in orange, MBV in green, BV in blue-green and PΦB in dark green): alternative chromophores to certain binding sites are indicated in brackets. Arrows pointing to tetrapyrrole binding sites represent identified lyases, with solid arrows indicating S-type lyases, dotted arrows T-type lyases and the dashed arrow E/F-type lyases. Boxed site numbers indicate correct autocatalytic binding, dotted boxes unclear situations. Vertical knobs indicate (partial) methylation at Asn-β72. Another PE, termed PE III, is not shown here. It has been identified in a high-light Prochlorococcus marinus, it carries only a single chromophore on the α-subunit, and none on the β-subunit (Hess et al., 1996). a, plant and most cyanobacterial phytochromes; b, bacterial, fungal and several cyanobacterial phytochromes; c, PE 545; d, only in red-algal b- (and possibly B-) PE. For biliprotein nomenclature, see Sidler (1994), Schluchter and Bryant (2002), and, alternatively (MacColl, 1998).

Mentions: Phycobiliproteins from cyanobacteria and red algae are a large, monophyletic family of homologous heterodimeric proteins. Both the α- and β-subunits, which are also homologous to each other, consist of a globin-type core that carries the chromophore(s), and an N-terminal extension that is mainly involved in oligomerization. The subunits form heterodimers, and these can further oligomerize to ring-shaped ‘trimers’ (heterohexamers) and ‘hexamers’ (heterododecamers) that constitute the building blocks of the unique extra-membraneous antenna complex, the PBS (Scheer, 1982; Ficner and Huber, 1993; Sidler, 1994; Ritter et al., 1999; Stec et al., 1999; Wang et al., 2001; Adir et al., 2002; Nield et al., 2003; Doust et al., 2004; Schmidt et al., 2007). Oligomerization is largely reduced in the apoproteins; therefore, chromophore attachment also seems a prerequisite for PBS assembly (Anderson and Toole, 1998). The hexameric building blocks are further arranged in short stacks that form the PBS core, or to longer rods that are attached to the former. This supramolecular organization is mainly due to linker proteins which are located, as a central backbone, in the inner triangular hole of the ring-shaped biliproteins (Tandeau de Marsac and Cohen-Bazire, 1977; Sidler, 1994; Apt et al., 1995; Reuter et al., 1999; Liu et al., 2005). Most of the linker proteins are colourless, but at least two of them also carry covalently bound chromophores, namely, the core-membrane linker Lcm (= ApcE), and the γ-subunits of class II and some class I phycoerythrins (PEs) (Fig. 1). However, crystal structures of these phycobiliproteins have not been solved. Other, less characterized biliproteins, are variants of unknown function (Montgomery et al., 2004), or the PE of certain Prochlorococcus species, marine picocyanobacteria that lack PBSs (Hess et al., 2001). Cryptophyte phycobiliproteins represent a second type of biliprotein antenna with different structure and organization (Sidler, 1994): the β-subunits are phylogenetically related to the β-subunits of red algal PEs, but the α-subunits are much shorter and probably of different origin. The phytochromes and related sensory photoreceptors that form yet another group of phylogenetically unrelated biliproteins generally carry only a single chromophore at one of two alternative binding sites (Lamparter, 2004; Ishizuka et al., 2007; Montgomery, 2007).


Biliprotein maturation: the chromophore attachment.

Scheer H, Zhao KH - Mol. Microbiol. (2008)

Post-translational modifications of biliproteins. Tetrapyrrole binding cysteines (consensus numbering2) with chromophores indicated in their approximate colours of the native chromoproteins (PCB in blue, PVB in purple, PEB in red, PUB in orange, MBV in green, BV in blue-green and PΦB in dark green): alternative chromophores to certain binding sites are indicated in brackets. Arrows pointing to tetrapyrrole binding sites represent identified lyases, with solid arrows indicating S-type lyases, dotted arrows T-type lyases and the dashed arrow E/F-type lyases. Boxed site numbers indicate correct autocatalytic binding, dotted boxes unclear situations. Vertical knobs indicate (partial) methylation at Asn-β72. Another PE, termed PE III, is not shown here. It has been identified in a high-light Prochlorococcus marinus, it carries only a single chromophore on the α-subunit, and none on the β-subunit (Hess et al., 1996). a, plant and most cyanobacterial phytochromes; b, bacterial, fungal and several cyanobacterial phytochromes; c, PE 545; d, only in red-algal b- (and possibly B-) PE. For biliprotein nomenclature, see Sidler (1994), Schluchter and Bryant (2002), and, alternatively (MacColl, 1998).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2327270&req=5

fig01: Post-translational modifications of biliproteins. Tetrapyrrole binding cysteines (consensus numbering2) with chromophores indicated in their approximate colours of the native chromoproteins (PCB in blue, PVB in purple, PEB in red, PUB in orange, MBV in green, BV in blue-green and PΦB in dark green): alternative chromophores to certain binding sites are indicated in brackets. Arrows pointing to tetrapyrrole binding sites represent identified lyases, with solid arrows indicating S-type lyases, dotted arrows T-type lyases and the dashed arrow E/F-type lyases. Boxed site numbers indicate correct autocatalytic binding, dotted boxes unclear situations. Vertical knobs indicate (partial) methylation at Asn-β72. Another PE, termed PE III, is not shown here. It has been identified in a high-light Prochlorococcus marinus, it carries only a single chromophore on the α-subunit, and none on the β-subunit (Hess et al., 1996). a, plant and most cyanobacterial phytochromes; b, bacterial, fungal and several cyanobacterial phytochromes; c, PE 545; d, only in red-algal b- (and possibly B-) PE. For biliprotein nomenclature, see Sidler (1994), Schluchter and Bryant (2002), and, alternatively (MacColl, 1998).
Mentions: Phycobiliproteins from cyanobacteria and red algae are a large, monophyletic family of homologous heterodimeric proteins. Both the α- and β-subunits, which are also homologous to each other, consist of a globin-type core that carries the chromophore(s), and an N-terminal extension that is mainly involved in oligomerization. The subunits form heterodimers, and these can further oligomerize to ring-shaped ‘trimers’ (heterohexamers) and ‘hexamers’ (heterododecamers) that constitute the building blocks of the unique extra-membraneous antenna complex, the PBS (Scheer, 1982; Ficner and Huber, 1993; Sidler, 1994; Ritter et al., 1999; Stec et al., 1999; Wang et al., 2001; Adir et al., 2002; Nield et al., 2003; Doust et al., 2004; Schmidt et al., 2007). Oligomerization is largely reduced in the apoproteins; therefore, chromophore attachment also seems a prerequisite for PBS assembly (Anderson and Toole, 1998). The hexameric building blocks are further arranged in short stacks that form the PBS core, or to longer rods that are attached to the former. This supramolecular organization is mainly due to linker proteins which are located, as a central backbone, in the inner triangular hole of the ring-shaped biliproteins (Tandeau de Marsac and Cohen-Bazire, 1977; Sidler, 1994; Apt et al., 1995; Reuter et al., 1999; Liu et al., 2005). Most of the linker proteins are colourless, but at least two of them also carry covalently bound chromophores, namely, the core-membrane linker Lcm (= ApcE), and the γ-subunits of class II and some class I phycoerythrins (PEs) (Fig. 1). However, crystal structures of these phycobiliproteins have not been solved. Other, less characterized biliproteins, are variants of unknown function (Montgomery et al., 2004), or the PE of certain Prochlorococcus species, marine picocyanobacteria that lack PBSs (Hess et al., 2001). Cryptophyte phycobiliproteins represent a second type of biliprotein antenna with different structure and organization (Sidler, 1994): the β-subunits are phylogenetically related to the β-subunits of red algal PEs, but the α-subunits are much shorter and probably of different origin. The phytochromes and related sensory photoreceptors that form yet another group of phylogenetically unrelated biliproteins generally carry only a single chromophore at one of two alternative binding sites (Lamparter, 2004; Ishizuka et al., 2007; Montgomery, 2007).

Bottom Line: The discovery of new activities for the latter lyases, and of new types of lyases, have reinvigorated research activities in the subject.So far, work has mainly concentrated on cyanobacterial phycobiliproteins.Methodological advances in the process, however, as well as the finding of often large numbers of homologues, opens new possibilities for research on the subsequent assembly/disassembly of the phycobilisome in cyanobacteria and red algae, on the assembly and organization of the cryptophyte light-harvesting system, on applications in basic research such as protein folding, and on the use of phycobiliproteins for labelling.

View Article: PubMed Central - PubMed

Affiliation: Department Biologie I, Universität München, Menzinger Strasse 67, D-80638 München, Germany.

ABSTRACT
Biliproteins are a widespread group of brilliantly coloured photoreceptors characterized by linear tetrapyrrolic chromophores, bilins, which are covalently bound to the apoproteins via relatively stable thioether bonds. Covalent binding stabilizes the chromoproteins and is mandatory for phycobilisome assembly; and, it is also important in biliprotein applications such as fluorescence labelling. Covalent binding has, on the other hand, also considerably hindered biliprotein research because autocatalytic chromophore additions are rare, and information on enzymatic addition by lyases was limited to a single example, an EF-type lyase attaching phycocyanobilin to cysteine-alpha84 of C-phycocyanin. The discovery of new activities for the latter lyases, and of new types of lyases, have reinvigorated research activities in the subject. So far, work has mainly concentrated on cyanobacterial phycobiliproteins. Methodological advances in the process, however, as well as the finding of often large numbers of homologues, opens new possibilities for research on the subsequent assembly/disassembly of the phycobilisome in cyanobacteria and red algae, on the assembly and organization of the cryptophyte light-harvesting system, on applications in basic research such as protein folding, and on the use of phycobiliproteins for labelling.

Show MeSH
Related in: MedlinePlus