The role of the local environment of engineered Tyr to Trp substitutions for probing the denaturation mechanism of FIS

Hypomorphic mutations in human DNA ligase IV lead to compromised DNA binding efficiency, hydrophobicity and thermal stability

Studies have shown that Lig4 syndrome mutations in DNA ligase IV (LigIV) are compromised in its function with residual level of double strand break ligation activity in vivo. It was speculated that Lig4 syndrome mutations adversely affect protein folding and stability. Though there are crystal structures of LigIV, there are no reports of crystal structures of Lig4 syndrome mutants and their biophysical characterization to date. Here, we have examined the conformational states, thermal stability, hydrophobicity and DNA binding efficiency of human DNA LigIV wild type and its hypomorphic mutants by far-UV circular dichroism, tyrosine and tryptophan fluorescence, and 1-anilino-8-naphthalene-sulfonate binding, dynamic light scattering, size exclusion chromatography, multi-angle light scattering and electrophoretic mobility shift assay. We show here that LigIV hypomorphic mutants have reduced DNA-binding efficiency, a shift in secondary structure content from the helical to random coil, marginal reduction in their thermal stability and increased hydrophobicity as compared to the wild-type LigIV.

Role of MERIT40 in stabilization of BRCA1 complex: a protein-protein interaction study

MERIT40 is a novel associate of the BRCA1-complex, thus play an essential role in DNA damage repair mechanism. It is the least implicit protein and its structural and functional aspects of regulating the stability of BRCA1-MERIT40 complex remain equivocal. Analysis of protein-protein interactions between BRCA1 and its cellular binding partners like ABRAXAS, RAP80 and MERIT40 would help to understand the role of protein complex integrity in DNA repair mechanism. The recombinant proteins were purified and their structural aspects were elucidated by spectroscopic methods. Interaction analysis was carried out to determine binding partners of MERIT40. MERIT40 showed interaction with bridging molecule, called ABRAXAS, thus generate a scaffold among various members which further stabilizes the entire complex. It acts as an adapter molecule by interacting with BRCA1-BRCT in non-phosphorylation dependent manner. The feature enlighten on structural and interaction profile of BRCA1-complex member to elucidate their role in complex stability and DNA repair process.

Structural and functional characterization of the MERIT40 to understand its role in DNA repair

MERIT40 (MEdiator of RAP80 Interaction and Targeting 40) is a novel associate of the BRCA1-complex and plays an essential role in DNA damage repair. It is the least characterized protein of BRCA1-complex and mainly responsible for maintaining the complex integrity. However, its structural and functional aspects of regulating the complex stability still remain elusive. Here, we carried out a comprehensive examination of MERIT40 biophysical properties and identified its novel interacting partner which would help to understand its role in BRCA1-complex. The recombinant protein was purified by affinity chromatography and unfolding pathway was determined using spectroscopic and calorimetric methods. Molecular model was generated using combinatorial approaches of modeling, and monomer-monomer docking was carried out to identify dimeric interface. Disordered region of MERIT40 was hatchet using trypsin and chymotrypsin to illustrate the existence of stable domain whose function was speculated through DALI search. Our findings suggest that MERIT40 forms a dimer in a concentration-independent manner. Its central region shows remarkable stability towards the protease digestion and has structural similarity with vWA-like region, a domain mainly present in complement activation factors. MERIT40 undergoes a three-state unfolding transition pathway with a dimeric intermediate. It interacts with adaptor molecule of BRCA1-complex, called ABRAXAS, thus help in extending the bridging interaction among various members which further stabilizes the whole complex. The results presented in this paper provide first-hand information on structural and folding behavior of MERIT40. These findings will help in elucidating the role of protein-protein interactions in stabilization of BRCA1-complex.