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K K Rodgers

Publications and source records attributed to K K Rodgers.

7 recordsLinked to original sources
PubMed2001

Identification of two topologically independent domains in RAG1 and their role in macromolecular interactions relevant to V(D)J recombination.

V(D)J recombination is instigated by the recombination-activating proteins RAG1 and RAG2, which catalyze site-specific DNA cleavage at the border of the recombination signal sequence (RSS). Although both proteins are required for activity, core RAG1 (the catalytically active region containing residues 384-1008 of 1040) alone displays binding specificity for the conserved heptamer and nonamer sequences of the RSS. The nonamer-binding region lies near the N terminus of core RAG1, whereas the heptamer-binding region has not been identified. Here, potential domains within core RAG1 were identified using limited proteolysis studies. An iterative procedure of DNA cloning, protein expression, and characterization revealed the presence of two topologically independent domains within core RAG1, referred to as the central domain (residues 528-760) and the C-terminal domain (residues 761-980). The domains do not include the nonamer-binding region but rather largely span the remaining relatively uncharacterized region of core RAG1. Characterization of macromolecular interactions revealed that the central domain bound to the RSS with specificity for the heptamer and contained the predominant binding site for RAG2. The C-terminal domain bound DNA cooperatively but did not show specificity for either conserved RSS element. This domain was also found to self-associate, implicating it as a dimerization domain within RAG1.

Animals↗
PubMed1999

A dimer of the lymphoid protein RAG1 recognizes the recombination signal sequence and the complex stably incorporates the high mobility group protein HMG2.

RAG1 and RAG2 are the two lymphoid-specific proteins required for the cleavage of DNA sequences known as the recombination signal sequences (RSSs) flanking V, D or J regions of the antigen-binding genes. Previous studies have shown that RAG1 alone is capable of binding to the RSS, whereas RAG2 only binds as a RAG1/RAG2 complex. We have expressed recombinant core RAG1 (amino acids 384-1008) in Escherichia coli and demonstrated catalytic activity when combined with RAG2. This protein was then used to determine its oligomeric forms and the dissociation constant of binding to the RSS. Electrophoretic mobility shift assays show that up to three oligomeric complexes of core RAG1 form with a single RSS. Core RAG1 was found to exist as a dimer both when free in solution and as the minimal species bound to the RSS. Competition assays show that RAG1 recognizes both the conserved nonamer and heptamer sequences of the RSS. Zinc analysis shows the core to contain two zinc ions. The purified RAG1 protein overexpressed in E.coli exhibited the expected cleavage activity when combined with RAG2 purified from transfected 293T cells. The high mobility group protein HMG2 is stably incorporated into the recombinant RAG1/RSS complex and can increase the affinity of RAG1 for the RSS in the absence of RAG2.

Animals↗
PubMed1997

Crystal structure of the RAG1 dimerization domain reveals multiple zinc-binding motifs including a novel zinc binuclear cluster.

The crystal structure of the dimerization domain of the V(D)J recombination-activating protein, RAG1, was solved using zinc anomalous scattering. The structure reveals an unusual combination of multi-class zinc-binding motifs, including a zinc RING finger and a C2H2 zinc finger, that together from a single structural domain. The domain also contains a unique zinc binuclear cluster in place of a normally mononuclear zinc site in the RING finger. Together, four zinc ions help organize the entire domain, including the two helices that form the dimer interface.

Binding Sites↗
PubMed1996

A zinc-binding domain involved in the dimerization of RAG1.

Recombination-activating gene 1 (RAG1), as well as RAG2, are the only lymphoid-specific genes required for V(D)J recombination. RAG1 protein contains a C3HC4 zinc-binding motif (zinc ring finger) that binds two zinc ions. We have found that RAG1 contains additional zinc-binding motifs in the form of two separate C2H2 zinc finger sequences. One of the zinc fingers, in combination with the C3HC4 subdomain, forms a highly specific dimerization domain. A combination of biophysical techniques has been used to determine the energetics of association, the overall shape of the dimerization domain, and the relative orientation of the monomeric subunits within the dimer. These results provide direct evidence that a C3HC4 motif is involved in a protein-protein interaction, in this case via homodimer formation. In addition, the observation that the dimerization domain includes multi-class zinc binding motifs, namely both a zinc finger and a C3HC4 subdomain, has important implications for other C3HC4-containing proteins. The position of this dimerization domain in the N-terminal third of the RAG1 sequence of 1040 amino acid residues may have a significant influence on the activities associated with the C-terminal domains of the protein.

Amino Acid Sequence↗
PubMed1994

DNA binding and bending by the transcription factors GAL4(62*) and GAL4(149*).

The DNA binding domain of the GAL4 transcription factor from yeast is located in the N-terminal 60 residues of the polypeptide of 881 amino acids. This domain binds 2 Zn ions, which form a binuclear cluster, Zn2C6, with 6 C residues, two of which bridge the 2 metal ions (Gardner KH et al., 1991, Biochemistry 30:11292-11302). Binding of Zn or Cd to GAL4 induces the conformation of the protein necessary to recognize the specific DNA sequence, UASG, to which GAL4 binds as a dimer. Gel retardation assays have been utilized to determine the relative affinities of the Zn2 and Zn1 forms of the N-terminal 149 residues of GAL4, GAL4(149*), for UASG DNA sequences. We show that Cd2- and Zn1GAL4(149*) bind to UASG DNA with 2-fold and 4-8-fold lower affinities than Zn2GAL4(149*), respectively. Thus, the metal species and the number of metal ions bound have measurable effects on the specific DNA binding affinity of GAL4, but these differences are small in comparison to the ratio, > 10(3) under some conditions, that characterizes the specific to nonspecific DNA binding affinities of the N-terminal fragments of GAL4. A shorter N-terminal fragment, GAL4(62*), although it continues to recognize the UASG sequence with a high degree of specificity, binds with 1,000-2,000-fold lower affinity than does Zn2GAL4(149*). Gel retardation titrations of a DNA containing 2 UASG sites with increasing concentrations of GAL4(62*) generate a series of 4 retarded bands in contrast to 2 retarded bands formed when the same DNA is titrated with GAL4(149*). These data suggest that GAL4(62*) binds to the UASG sites as individual monomers that dimerize on the DNA, whereas GAL4(149*) binds the UASG DNA cooperatively as a dimer. The approximately 10(3) lower affinity of GAL4(62*) for the UASG DNA can be accounted for by its failure to form dimers in solution. Zn2-, Zn1-, or Cd2GAL4(149*) induces differential rates of gel migration in a series of circularly permutated UASG-containing DNA restriction fragments. Analysis of the data suggests that all 3 proteins cause a 26 degrees angle of bend in the DNA when bound to 1 UASG site and 45 degrees when bound to 2 tandem UASG sites. The same assay shows that GAL4(62*) does not induce significant bending of the UASG DNA sequences. Thus, the additional subdomains found in the larger polypeptide fragment, GAL4(149*), must exert an additional force on the DNA either through direct contacts with the DNA or indirectly through altered protein conformation.

Base Sequence↗
PubMed1991

Mapping electrostatic interactions in macromolecular associations.

In the association of electron transfer proteins, electrostatics has been proposed to play a role in maintaining the stability and specificity of the biomolecular complexes formed. An excellent model system is the interaction between mammalian cytochrome b5 and cytochrome c, in which the X-ray structures of the individual components reveal a complementary asymmetry of charges surrounding their respective redox centers. Determining the exact extent of the electrostatic interactions and identifying the specific residues involved in the formation of the electron transfer complex has proved more elusive. We report herein the utilization of high-pressure techniques, together with site-directed mutagenesis, to provide a map of the interaction domains in biomolecular complex formation. The application of high pressure disrupts macromolecular associations since dissociation of the complex results in a decreased volume of the system due to the solvation of charges that had been previously sequestered in the interface region and force solvation of hydrophobic surfaces. Site-directed mutagenesis of a totally synthetic gene for rat liver cytochrome b5, which expresses this mammalian protein in Escherichia coli as a hemecontaining soluble component, was used to selectively alter negatively charged residues of cytochrome b5 to neutral amide side-chains. We have demonstrated that the interaction domain of cytochrome b5 with cytochrome c can be mapped from a comparison of dissociation volumes of these modified cytochrome b5-cytochrome c complexes with the native complex. Using these techniques we can specifically investigate the role of particular residues in the equilibrium association of these two electron transfer proteins. Single-point mutations in the interaction domain give nearly identical effects on the measured dissociation volumes, yet removal of acidic residues outside the recognition surface yield volumes similar to wild-type protein. Multiple mutations in the proposed protein-protein interaction site are found to allow greater solvent-accessibility of the interface as reflected in a diminution in the volume changes on subsequent charge removal. This is indicative that the interprotein salt-bridges in this complex provide a mechanism for a greater exclusion of solvent from the interfacial domain of the complex, resulting in a more stable association.

Amino Acids↗
PubMed1988

Probing the mechanisms of macromolecular recognition: the cytochrome b5-cytochrome c complex.

The specificity of complex formation between cytochrome b5 (cyt b5) and cytochrome c (cyt c) is believed to involve the formation of salt linkages between specific carboxylic acid residues of cyt b5 with lysine residues on cyt c. Site-directed mutagenesis was used to alter the specified acidic residues of cyt b5 to the corresponding amide analogues, which resulted in a lower affinity for complex formation with cyt c. The dissociation of the complex under high pressure resulted in specific volume changes, the magnitude of which reflected the degree of solvation of the acidic residues in the proposed protein-protein interface.

Animals↗