Biomedical subjects

Klemens Wild

Publications and source records attributed to Klemens Wild.

6 recordsLinked to original sources

PubMed2006

The structure of the mammalian signal recognition particle (SRP) receptor as prototype for the interaction of small GTPases with Longin domains.

The eukaryotic signal recognition particle (SRP) and its receptor (SR) play a central role in co-translational targeting of secretory and membrane proteins to the endoplasmic reticulum. The SR is a heterodimeric complex assembled by the two GTPases SRalpha and SRbeta, which is membrane-anchored. Here we present the 2.45-A structure of mammalian SRbeta in its Mg2+ GTP-bound state in complex with the minimal binding domain of SRalpha termed SRX. SRbeta is a member of the Ras-GTPase superfamily closely related to Arf and Sar1, while SRX belongs to the SNARE-like superfamily with a fold also known as longin domain. SRX binds to the P loop and the switch regions of SRbeta-GTP. The binding mode and structural similarity with other GTPase-effector complexes suggests a co-GAP (GTPase-activating protein) function for SRX. Comparison with the homologous yeast structure and other longin domains reveals a conserved adjustable hydrophobic surface within SRX which is of central importance for the SRbeta-GTP:SRX interface. A helix swap in SRX results in the formation of a dimer in the crystal structure. Based on structural conservation we present the SRbeta-GTP:SRX structure as a prototype for conserved interactions in a variety of GTPase regulated targeting events occurring at endomembranes.

Affinity Labels↗

PubMed2004

SRP meets the ribosome.

Cotranslational targeting directly couples synthesis of proteins to their translocation across or insertion into membranes. The signal recognition particle (SRP) and its membrane-bound receptor facilitate the targeting of the translation machinery, the ribosome, via recognition of a signal sequence in the nascent peptide chain. By combining structures of free and ribosome-bound SRP we derive a structural model describing the dynamic nature of SRP when it meets the ribosome.

Animals↗

PubMed2004

A structural step into the SRP cycle.

Co-translational targeting of secretory and membrane proteins to the translocation machinery is mediated by the signal recognition particle (SRP) and its membrane-bound receptor (SR) in all three domains of life. Although the overall composition of the SRP system differs, the central ribonucleoprotein core and the general mechanism of GTP-dependent targeting are highly conserved. Recently, structural studies have contributed significantly to our understanding of the molecular organization of SRP. SRP appears as a structurally flexible particle modulated and regulated by its interactions with the ribosome-nascent chain complex, the translocon and the SR. The SRP core (SRP54 with its cognate RNA binding site) plays a central role in these interactions and communicates the different binding states by long-range interdomain communication. Based on recent structures of SRP54, a model for signal peptide binding stimulating the GTP affinity during the first step of the SRP cycle is presented. The model is placed in the context of the recent structures of mammalian SRP bound to a ribosome-nascent chain complex and of a subcomplex of SRP-SR.

Guanosine Triphosphate↗

PubMed2003

Crystallization of the crenarchaeal SRP core.

Protein translocation across or targeting to membranes mediated by the signal recognition particle (SRP) is a universal mechanism conserved in all domains of life. SRP54 from the crenarchaeon Sulfolobus solfataricus has been recombinantly expressed and crystallized with and without SRP RNA helix 8. The RNA has been transcribed in vitro using ribozyme technology. Both crystal forms are perfect merohedral twins. While SRP54 alone is hemihedrally twinned, the crystals of the SRP54-helix 8 complex indicate tetartohedral twinning, which has not previously been observed in protein crystals. The tetartohedral twinning is enabled by a special diamond-like packing in a trigonal crystal.

Archaeal Proteins↗

PubMed2003

Crystal structure of the complete core of archaeal signal recognition particle and implications for interdomain communication.

Targeting of secretory and membrane proteins by the signal recognition particle (SRP) is evolutionarily conserved, and the multidomain protein SRP54 acts as the key player in SRP-mediated protein transport. Binding of a signal peptide to SRP54 at the ribosome is coordinated with GTP binding and subsequent complex formation with the SRP receptor. Because these functions are localized to distinct domains of SRP54, communication between them is essential. We report the crystal structures of SRP54 from the Archaeon Sulfolobus solfataricus with and without its cognate SRP RNA binding site (helix 8) at 4-A resolution. The two structures show the flexibility of the SRP core and the position of SRP54 relative to the RNA. A long linker helix connects the GTPase (G domain) with the signal peptide binding (M) domain, and a hydrophobic contact between the N and M domains relates the signal peptide binding site to the G domain. Hinge regions are identified in the linker between the G and M domains (292-LGMGD) and in the N-terminal part of the M domain, which allow for structural rearrangements within SRP54 upon signal peptide binding at the ribosome.

Amino Acid Sequence↗

PubMed2002

Towards the structure of the mammalian signal recognition particle.

The signal recognition particle (SRP) is a ubiquitous ribonucleoprotein particle involved in the co-translational targeting of proteins to membranes. Crystal structures are now available for three protein-RNA subcomplexes from the SRP, which give insights into fundamental aspects of protein-RNA recognition, the assembly of stable ribonucleoprotein particles and the mechanism of action of the SRP.

Alu Elements↗