Project description:OSR1 (oxidative stress-responsive-1) and SPAK (Ste20/Sps1-related proline/alanine-rich kinase) belong to the GCK-VI subfamily of Ste20 group kinases. OSR1 and SPAK are key regulators of NKCCs (Na(+)/K(+)/2Cl(-) cotransporters) and activated by WNK family members (with-no-lysine kinase), mutations of which are known to cause Gordon syndrome, an autosomal dominant form of inherited hypertension. The crystal structure of OSR1 kinase domain has been solved at 2.25 A. OSR1 forms a domain-swapped dimer in an inactive conformation, in which P+1 loop and alphaEF helix are swapped between dimer-related monomers. Structural alignment with nonswapped Ste20 TAO2 kinase indicates that the integrity of chemical interactions in the kinase domain is well preserved in the domain-swapped interfaces. The OSR1 kinase domain has now been added to a growing list of domain-swapped protein kinases recently reported, suggesting that the domain-swapping event provides an additional layer of complexity in regulating protein kinase activity.
Project description:The related protein kinases SPAK and OSR1 regulate ion homeostasis in part by phosphorylating cation cotransporter family members. The structure of the kinase domain of OSR1 was determined in the unphosphorylated inactive form and, like some other Ste20 kinases, exhibited a domain-swapped activation loop. To further probe the role of domain swapping in SPAK and OSR1, we have determined the crystal structures of SPAK 63-403 at 3.1 Å and SPAK 63-390 T243D at 2.5 Å resolution. These structures encompass the kinase domain and different portions of the C-terminal tail, the longer without and the shorter with an activating T243D point mutation. The structure of the T243D protein reveals significant conformational differences relative to unphosphorylated SPAK and OSR1 but also has some features of an inactive kinase. Both structures are domain-swapped dimers. Sequences involved in domain swapping were identified and mutated to create a SPAK monomeric mutant with kinase activity, indicating that monomeric forms are active. The monomeric mutant is activated by WNK1 but has reduced activity toward its substrate NKCC2, suggesting regulatory roles for domain swapping. The structure of partially active SPAK T243D is consistent with a multistage activation process in which phosphorylation induces a SPAK conformation that requires further remodeling to build the active structure.
Project description:Two monofunctional Delta(3), Delta(2)-enoyl-CoA isomerases, one in mitochondria (mECI) and the other in both mitochondria and peroxisomes (pECI), belong to the low-similarity isomerase/hydratase superfamily. Both enzymes catalyze the movement of a double bond from C3 to C2 of an unsaturated acyl-CoA substrate for re-entry into the beta-oxidation pathway. Mutagenesis has shown that Glu165 of rat mECI is involved in catalysis; however, the putative catalytic residue in yeast pECI, Glu158, is not conserved in mECI. To elucidate whether Glu165 of mECI is correctly positioned for catalysis, the crystal structure of rat mECI has been solved. Crystal packing suggests the enzyme is trimeric, in contrast to other members of the superfamily, which appear crystallographically to be dimers of trimers. The polypeptide fold of mECI, like pECI, belongs to a subset of this superfamily in which the C-terminal domain of a given monomer interacts with its own N-terminal domain. This differs from that of crotonase and 1,4-dihydroxy-2-naphtoyl-CoA synthase, whose C-terminal domains are involved in domain swapping with an adjacent monomer. The structure confirms Glu165 as the putative catalytic acid/base, positioned to abstract the pro-R proton from C2 and reprotonate at C4 of the acyl chain. The large tunnel-shaped active site cavity observed in the mECI structure explains the relative substrate promiscuity in acyl-chain length and stereochemistry. Comparison with the crystal structure of pECI suggests the catalytic residues from both enzymes are spatially conserved but not in their primary structures, providing a powerful reminder of how catalytic residues cannot be determined solely by sequence alignments.
Project description:For several different proteins an apparent correlation has been observed between the propensity for dimerization by domain-swapping and the ability to aggregate into amyloid-like fibrils. Examples include the disease-related proteins β 2-microglobulin and transthyretin. This has led to proposals that the amyloid-formation pathway may feature extensive domain swapping. One possible consequence of such an aggregation pathway is that the resulting fibrils would incorporate structural elements that resemble the domain-swapped forms of the protein and, thus, reflect certain native-like structures or domain-interactions. In magic angle spinning solid-state NMR-based and other structural studies of such amyloid fibrils, it appears that many of these proteins form fibrils that are not native-like. Several fibrils, instead, have an in-register, parallel conformation, which is a common amyloid structural motif and is seen, for instance, in various prion fibrils. Such a lack of native structure in the fibrils suggests that the apparent connection between domain-swapping ability and amyloid-formation may be more subtle or complex than may be presumed at first glance.
Project description:Tandem homologous domains in proteins are susceptible to misfolding through the formation of domain swaps, non-native conformations involving the exchange of equivalent structural elements between adjacent domains. Cutting-edge biophysical experiments have recently allowed the observation of tandem domain swapping events at the single molecule level. In addition, computer simulations have shed light into the molecular mechanisms of domain swap formation and serve as the basis for methods to systematically predict them. At present, the number of studies on tandem domain swaps is still small and limited to a few domain folds, but they offer important insights into the folding and evolution of multidomain proteins with applications in the field of protein design.
Project description:SgrAI is a type IIF restriction endonuclease that cuts an unusually long recognition sequence and exhibits allosteric self-modulation of cleavage activity and sequence specificity. Previous studies have shown that DNA bound dimers of SgrAI oligomerize into an activated form with higher DNA cleavage rates, although previously determined crystal structures of SgrAI bound to DNA show only the DNA bound dimer. A new crystal structure of the type II restriction endonuclease SgrAI bound to DNA and Ca(2+) is now presented, which shows the close association of two DNA bound SgrAI dimers. This tetrameric form is unlike those of the homologous enzymes Cfr10I and NgoMIV and is formed by the swapping of the amino-terminal 24 amino acid residues. Two mutations predicted to destabilize the swapped form of SgrAI, P27W and P27G, have been made and shown to eliminate both the oligomerization of the DNA bound SgrAI dimers as well as the allosteric stimulation of DNA cleavage by SgrAI. A mechanism involving domain swapping is proposed to explain the unusual allosteric properties of SgrAI via association of the domain swapped tetramer of SgrAI bound to DNA into higher order oligomers.
Project description:Three-dimensional (3D) domain swapping creates a bond between two or more protein molecules as they exchange their identical domains. Since the term '3D domain swapping' was first used to describe the dimeric structure of diphtheria toxin, the database of domain-swapped proteins has greatly expanded. Analyses of the now about 40 structurally characterized cases of domain-swapped proteins reveal that most swapped domains are at either the N or C terminus and that the swapped domains are diverse in their primary and secondary structures. In addition to tabulating domain-swapped proteins, we describe in detail several examples of 3D domain swapping which show the swapping of more than one domain in a protein, the structural evidence for 3D domain swapping in amyloid proteins, and the flexibility of hinge loops. We also discuss the physiological relevance of 3D domain swapping and a possible mechanism for 3D domain swapping. The present state of knowledge leads us to suggest that 3D domain swapping can occur under appropriate conditions in any protein with an unconstrained terminus. As domains continue to swap, this review attempts not only a summary of the known domain-swapped proteins, but also a framework for understanding future findings of 3D domain swapping.
Project description:The same energy landscape principles associated with the folding of proteins into their monomeric conformations should also describe how these proteins oligomerize into domain-swapped conformations. We tested this hypothesis by using a simplified model for the epidermal growth factor receptor pathway substrate 8 src homology 3 domain protein, both of whose monomeric and domain-swapped structures have been solved. The model, which we call the symmetrized Gō-type model, incorporates only information regarding the monomeric conformation in an energy function for the dimer to predict the domain-swapped conformation. A striking preference for the correct domain-swapped structure was observed, indicating that overall monomer topology is a main determinant of the structure of domain-swapped dimers. Furthermore, we explore the free energy surface for domain swapping by using our model to characterize the mechanism of oligomerization.
Project description:The oxidative-stress-responsive kinase 1 (OSR1) and the STE20/SPS1-related proline/alanine-rich kinase (SPAK) are key enzymes in a signaling cascade regulating the activity of Na(+)-K(+)-2Cl(-) cotransporters (NKCC1-2) and Na(+)-Cl(-) cotransporter (NCC). Both kinases have a conserved carboxyl-terminal (CCT) domain, which recognizes a unique peptide motif present in OSR1- and SPAK-activating kinases (with-no-lysine kinase 1 (WNK1) and WNK4) as well as their substrates (NKCC1, NKCC2, and NCC). Utilizing various modalities of the Rosetta Molecular Modeling Software Suite including flexible peptide docking and protein design, we comprehensively explored the sequence space recognized by the CCT domain. Specifically, we studied single residue mutations as well as complete unbiased designs of a hexapeptide substrate. The computational study started from a crystal structure of the CCT domain of OSR1 in complex with a hexapeptide derived from WNK4. Point mutations predicted to be favorable include Arg to His or Trp substitutions at position 2 and a Phe to Tyr substitution at position 3 of the hexapeptide. In addition, de novo design yielded two peptides predicted to bind to the CCT domain: FRFQVT and TRFDVT. These results, which indicate a little bit more freedom in the composition of the peptide, were confirmed through the use of yeast two-hybrid screening.