The Arabidopsis COP1/SPA complex is a key repressor of photomorphogenesis that suppresses light signaling in the dark. Both COP1 and SPA proteins are essential components of this complex. Although COP1 also exists in humans, SPA genes are specific to the green lineage.To elucidate the evolution of SPA genes we analyzed SPA functions in the moss Physcomitrella patens by characterizing knockout mutants in the two Physcomitrella SPA genes PpSPAa and PpSPAb.Light-grown PpspaAB double mutants exhibit smaller gametophores than the wild-type. In the dark, PpspaAB mutant gametophores show enhanced continuation of growth but etiolate normally. Gravitropism in the dark is reduced in PpspaAB mutant protonemata. The expression of light-regulated genes is mostly not constitutive in PpspaAB mutants. PpSPA and PpCOP1 interact; PpCOP1 also interacts with the transcription factor PpHY5 and, indeed, PpHY5 is destabilized in dark-grown Physcomitrella. Degradation of PpHY5 in darkness, however, does not require PpSPAa and PpSPAb.The data suggest that COP1/SPA-mediated light signaling is only partially conserved between Arabidopsis and Physcomitrella. Whereas COP1/SPA interaction and HY5 degradation in darkness is conserved, the role of SPA proteins appears to have diverged. PpSPA genes, unlike their Arabidopsis counterparts, are only required to suppress a subset of light responses in darkness.

Collagen model peptides (CMPs) serve as tools for understanding stability and function of the collagen triple helix and have a potential for biomedical applications. In the past, interstrand cross‐linking or conformational preconditioning of proline units through stereoelectronic effects have been utilized in the design of stabilized CMPs. To further study the effects determining collagen triple helix stability we investigated a series of CMPs containing synthetic diproline‐mimicking modules (ProMs), which were preorganized in a PPII‐helix‐type conformation by a functionalizable intrastrand C2 bridge. Results of CD‐based denaturation studies were correlated with calculated (DFT) conformational preferences of the ProM units, revealing that the relative helix stability is mainly governed by an interplay of main‐chain preorganization, ring‐flip preference, adaptability, and steric effects. Triple helix integrity was proven by crystal structure analysis and binding to HSP47.

Distinct families of eukaryotic deubiquitinases (DUBs) are regulators of ubiquitin signaling. Here, we report on the presence of an additional DUB class broadly distributed in eukaryotes and several bacteria. The only described members of this family are the large tegument proteins of herpesviruses, which are attached to the outside of the viral capsid. By using a bioinformatics screen, we have identified distant homologs of this VTD (Viral tegument-like DUB) family in vertebrate transposons, fungi, insects, nematodes, cnidaria, protists and bacteria. While some VTD activities resemble viral tegument DUBs in that they favor K48-linked ubiquitin chains, other members are highly specific for K6- or K63-linked ubiquitin chains. The crystal structures of K48- and K6-specific members reveal considerable differences in ubiquitin recognition. The VTD family likely evolved from non-DUB proteases and spread through transposons, many of which became ‘domesticated’, giving rise to the Drosophila male sterile (3)76Ca gene and several nematode genes with male-specific expression.

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Collagen model peptides (CMPs) serve as tools for understanding stability and function of the collagen triple helix and have a potential for biomedical applications. In the past, interstrand cross‐linking or conformational preconditioning of proline units through stereoelectronic effects have been utilized in the design of stabilized CMPs. To further study the effects determining collagen triple helix stability we investigated a series of CMPs containing synthetic diproline‐mimicking modules (ProMs), which were preorganized in a PPII‐helix‐type conformation by a functionalizable intrastrand C2 bridge. Results of CD‐based denaturation studies were correlated with calculated (DFT) conformational preferences of the ProM units, revealing that the relative helix stability is mainly governed by an interplay of main‐chain preorganization, ring‐flip preference, adaptability, and steric effects. Triple helix integrity was proven by crystal structure analysis and binding to HSP47.

Several distinct families of eukaryotic deubiquitinases (DUBs) regulate various aspects of ubiquitin signaling. Apart from one metalloenzyme family, six classes of eukaryotic papain-fold cysteine proteases are known to have DUB activity. A seventh cysteine-based DUB class is found in intracellular bacteria, which use DUB effectors to evade the ubiquitin-based defense response. Here, we report on the presence of an additional DUB class broadly distributed in eukaryotes and several bacteria. So far, the only known members of this family are the large tegument proteins of α/β/γ herpesviruses, which act as relatively unspecific deubiquitinases and deneddylases attached to the outer face of the viral capsid. By using a bioinformatical screen, we identified distant homologs of this family in transposons of vertebrates and invertebrates, in agaricomycete fungi, insects, nematodes, cnidaria, protists and selected intracellular bacteria. Members of this VTD (Viral tegument-like DUB) family use an atypical Cys-Asp-His catalytic triad to cleave ubiquitin chains. Some activities resemble the viral tegument DUBs in preferring K48-linked ubiquitin chains and also cleaving NEDD8, while other members are highly specific for K6- or K63-linked ubiquitin chains. Judging by the crystal structures of K48- and K6-specific members, the subfamilies differ considerably in their ubiquitin recognition mode. Our analyses suggest that this deubiquitinase family evolved from YopT/HopN-like non-DUB proteases and was co-opted early by DNA transposons, helping the spread of this family. In several independent events, the deubiquitinase domain of these transposons was ‘domesticated’ by various taxa, giving rise e.g. to the Drosophila male sterile (3)76Ca gene and several nematode genes with male-specific expression.

No abstract