Result and Discussions
3.1. Changes in catalytic pocket
Instead of having the conventional catalytic triad residues (His665, His667 and Asp767) in it’s protease domain, Lon protease employs the Ser679 – Lys722 catalytic dyad to form a catalytic pocket for promoting proteolysis. But the mutations in catalytic dyad residues make some changes in the catalytic pocket of these three mutant types.
A comparison of SASA values and RSA values [Supplementary file 1] were done among the catalytic pockets of wild type Lon protease and the three different mutant types of Lon protease. The catalytic pocket of wild type Lon protease shows a SASA value of 5840.7Å.
In case of K722Q and S679A mutation, the SASA values of catalytic pocket are 5932.97Å and …show more content…
To promote proteolysis, Lon protease recognizes α- crystalin domain of IbpA and IbpB and interacts with it. In each of the mutant type Lon protease, the mutation in the catalytic dyad residue disables the Lon protease to promote proteolysis. Due to each of this mutation, the catalytic pocket fails to recognize the α- crystalin domain of IbpA and IbpB and to interact with them for proteolytic initiation which contributes in a change of SASA value in each of the mutant type Lon protease in comparison to the wild type Lon protease.
Superimposition of the catalytic pocket of wild type Lon protease with K722Q mutant, S679A mutant and double mutant Lon protease generates a RMSD difference of 1.38Å, 1.39Å and 1.67Å respectively. This significant difference in RMSD value along with SASA value and RSA value clearly states that these mutations of the catalytic dyad residues (S679A , K722Q & double mutant) changes the shape of the catalytic pockets which affect the solvent accessibility and proteolytic activity of mutant Lon protease.
3.2. Changes in the binding …show more content…
In wild type complex, Lon interacts with IbpB much more than IbpA whereas in each of the mutant type complex, Lon interacts almost equally with IbpA and IbpB. Lon can equally recognize these two proteins but processes IbpB much faster than IbpA for proteolytic mechanism. The tails of IbpA protein actually inhibits Lon degradation, so Lon recognizes both these IbpA and IbpB equally but interacts as well as processes IbpB more as IbpB tails do not impose any inhibition to degradation. So, in wild type, to initiate proteolytic degradation, Lon interacts with IbpB more spontaneously. But in cases of these mutant types, as the catalytic dyad residues are mutated (K7722Q, S679A & double mutant), these mutant proteases can recognize the small heat shock proteins but become unable to degrade them Actually, as each of these mutations affects the proteolytic activity of Lon protease, the mutant Lon interacts with these two substrates but does not initiate the processing of these two proteins and so despite of interacting with IbpB more, it interacts with IbpA and IbpB in almost equal fashion without any proteolytic
3.1. Changes in catalytic pocket
Instead of having the conventional catalytic triad residues (His665, His667 and Asp767) in it’s protease domain, Lon protease employs the Ser679 – Lys722 catalytic dyad to form a catalytic pocket for promoting proteolysis. But the mutations in catalytic dyad residues make some changes in the catalytic pocket of these three mutant types.
A comparison of SASA values and RSA values [Supplementary file 1] were done among the catalytic pockets of wild type Lon protease and the three different mutant types of Lon protease. The catalytic pocket of wild type Lon protease shows a SASA value of 5840.7Å.
In case of K722Q and S679A mutation, the SASA values of catalytic pocket are 5932.97Å and …show more content…
To promote proteolysis, Lon protease recognizes α- crystalin domain of IbpA and IbpB and interacts with it. In each of the mutant type Lon protease, the mutation in the catalytic dyad residue disables the Lon protease to promote proteolysis. Due to each of this mutation, the catalytic pocket fails to recognize the α- crystalin domain of IbpA and IbpB and to interact with them for proteolytic initiation which contributes in a change of SASA value in each of the mutant type Lon protease in comparison to the wild type Lon protease.
Superimposition of the catalytic pocket of wild type Lon protease with K722Q mutant, S679A mutant and double mutant Lon protease generates a RMSD difference of 1.38Å, 1.39Å and 1.67Å respectively. This significant difference in RMSD value along with SASA value and RSA value clearly states that these mutations of the catalytic dyad residues (S679A , K722Q & double mutant) changes the shape of the catalytic pockets which affect the solvent accessibility and proteolytic activity of mutant Lon protease.
3.2. Changes in the binding …show more content…
In wild type complex, Lon interacts with IbpB much more than IbpA whereas in each of the mutant type complex, Lon interacts almost equally with IbpA and IbpB. Lon can equally recognize these two proteins but processes IbpB much faster than IbpA for proteolytic mechanism. The tails of IbpA protein actually inhibits Lon degradation, so Lon recognizes both these IbpA and IbpB equally but interacts as well as processes IbpB more as IbpB tails do not impose any inhibition to degradation. So, in wild type, to initiate proteolytic degradation, Lon interacts with IbpB more spontaneously. But in cases of these mutant types, as the catalytic dyad residues are mutated (K7722Q, S679A & double mutant), these mutant proteases can recognize the small heat shock proteins but become unable to degrade them Actually, as each of these mutations affects the proteolytic activity of Lon protease, the mutant Lon interacts with these two substrates but does not initiate the processing of these two proteins and so despite of interacting with IbpB more, it interacts with IbpA and IbpB in almost equal fashion without any proteolytic