Lamin A protein, encoded by the LMNA gene, belongs to the type V intermediate filament protein family and is a major nuclear protein component of higher metazoan organisms, including humans. Lamin A along with B-type lamins impart structural rigidity to the nucleus by forming a lamina that is closely apposed to the inner nuclear membrane and is also present as a filamentous network in the interior of the nucleus. A vast number of mutations that lead to a diverse array of at least 11 diseases in humans, collectively termed laminopathies, are being gradually uncovered in the LMNA gene. Dilated cardiomyopathy (DCM) is one such laminopathy in which ventricular dilation leads to an increase in systolic and diastolic volumes, resulting in cardiac arrhythmia and ultimately myocardial infarction. The point mutations in lamin A protein span the entire length of the protein, with a slight preponderance in the central α-helical coiled-coil forming domain. In this work, we have focused on three such important mutations that had been previously observed in DCM-afflicted patients producing severe symptoms. This is the first report to show that these mutations entail significant alterations in the secondary and tertiary structure of the protein, hence perturbing the intrinsic self-association behavior of lamin A protein. Comparison of the enthalpy changes accompanying the deoligomerization process for the wild type and the mutants suggests a difference in the energetics of their self-association. This is further corroborated by the formation of the aggregates of different size and distribution formed inside the nuclei of transfected cells.

Lamins are intermediate filament proteins of type V constituting a nuclear lamina or filamentous meshwork which lines the nucleoplasmic side of the inner nuclear membrane. This protein mesh provides a supporting scaffold for the nuclear envelope and tethers interphase chromosome to the nuclear periphery. Mutations of mainly A-type lamins are found to be causative for at least 11 human diseases collectively termed as laminopathies majority of which are characterised by aberrant nuclei with altered structural rigidity, deformability and poor mechanotransduction behaviour. But the investigation of viscoelastic behavior of lamin A continues to elude the field. In order to address this problem, we hereby present the very first report on viscoelastic properties of wild type human lamin A and some of its mutants linked with Dilated cardiomyopathy (DCM) using quantitative rheological measurements. We observed a dramatic strain-softening effect on lamin A network as an outcome of the strain amplitude sweep measurements which could arise from the large compliance of the quasi-cross-links in the network or that of the lamin A rods. In addition, the drastic stiffening of the differential elastic moduli on superposition of rotational and oscillatory shear stress reflect the increase in the stiffness of the laterally associated lamin A rods. These findings present a preliminary insight into distinct biomechanical properties of wild type lamin A protein and its mutants which in turn revealed interesting differences.

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Lamin B1 is one of the major constituents of the nuclear lamina, a filamentous network underlying the nucleoplasmic side of the inner nuclear membrane. Homopolymerization of lamin B1, coupled to the homotypic and heterotypic association of other lamin types, is central to building the higher order network pattern inside the nucleus. This in turn maintains the mechanical and functional integrity of the lamina. We have characterized the molecular basis of the self-association of lamin B1 using spectroscopic and calorimetric methods. We report that concentration dependent lamin B1 oligomerization involves significant alterations in secondary and tertiary structures of the protein resulting in fairly observable compaction in size. Comparison of the energetics of the homotypic association of lamin B1 with that of lamin A reported earlier led to the finding that lamin A oligomers had higher thermodynamic stability. This leads us to conjecture that lamin B1 has less stress bearing ability compared to lamin A.

Pandemic COVID-19 outbreak has been caused due to SARS-COV2 pathogen, resulting millions of infection and death worldwide, USA being on top at the present moment. The long, complex orf1ab polyproteins of SARS-COV2 play an important role in viral RNA synthesis. To assess the impact of mutations in this important domain, we analyzed 1134 complete protein sequences of orf1ab polyprotein from NCBI Virus database from affected patients across various states of USA from December 2019 to 25 th April, 2020. Multiple sequence alignment using Clustal Omega followed by statistical significance was calculated. Four significant mutations T265I (nsp 2), P4715L (nsp 12) and P5828L and Y5865C (both at nsp 13) were identified in important non-structural proteins, which function either as replicase or helicase. A comparative analysis shows 265T>I, 5828P>L and 5865Y>C are unique to USA and not reported from Europe or Asia; while one, 4715P>L is predominant in both Europe and USA. Mutational changes in amino acids are predicted to alter structure and function of corresponding proteins, thereby it is imperative to consider the mutational spectra while designing new antiviral therapeutics targeting viral orf1ab.