@article {2542, title = {DDX24 is required for muscle fiber organization and the suppression of wound-induced Wnt activity necessary for pole re-establishment during planarian regeneration.}, journal = {Dev Biol}, volume = {488}, year = {2022}, month = {2022 May 04}, pages = {11-29}, abstract = {

Planarians have a remarkable ability to undergo whole-body regeneration. Successful regeneration outcome is determined by processes like polarity establishment at the wound site, which is followed by pole (organizer) specification. Interestingly, these determinants are almost exclusively expressed by muscles in these animals. However, the molecular toolkit that enables the functional versatility of planarian muscles remains poorly understood. Here we report that SMED_DDX24, a D-E-A-D Box RNA helicase, is necessary for planarian survival and regeneration. We found that DDX24 is enriched in muscles and its knockdown disrupts muscle fiber organization. This leads to defective pole specification, which in turn results in misregulation of many positional control genes specifically during regeneration. ddx24 RNAi also upregulates wound-induced Wnt signalling. Suppressing this ectopic Wnt activity rescues the knockdown phenotype by enabling better anterior pole regeneration. To summarize, our work highlights the role of an RNA helicase in muscle fiber organization, and modulating amputation-induced wnt levels, both of which seem critical for pole re-organization, thereby regulating whole-body regeneration.

}, issn = {1095-564X}, doi = {10.1016/j.ydbio.2022.04.011}, author = {Sarkar, Souradeep R and Dubey, Vinay Kumar and Jahagirdar, Anusha and Lakshmanan, Vairavan and Haroon, Mohamed Mohamed and Sowndarya, Sai and Sowdhamini, Ramanathan and Palakodeti, Dasaradhi} } @article {1843, title = {Molecular basis for metabolite channeling in a ring opening enzyme of the phenylacetate degradation pathway.}, journal = {Nat Commun}, volume = {10}, year = {2019}, month = {2019 Sep 11}, pages = {4127}, abstract = {

Substrate channeling is a mechanism for the internal transfer of hydrophobic, unstable or toxic intermediates from the active site of one enzyme to another. Such transfer has previously been described to be mediated by a hydrophobic tunnel, the use of electrostatic highways or pivoting and by conformational changes. The enzyme PaaZ is used by many bacteria to degrade environmental pollutants. PaaZ is a bifunctional enzyme that catalyzes the ring opening of oxepin-CoA and converts it to 3-oxo-5,6-dehydrosuberyl-CoA. Here we report the structures of PaaZ determined by electron cryomicroscopy with and without bound ligands. The structures reveal that three domain-swapped dimers of the enzyme form a trilobed structure. A combination of small-angle X-ray scattering (SAXS), computational studies, mutagenesis and microbial growth experiments suggests that the key intermediate is transferred from one active site to the other by a mechanism of electrostatic pivoting of the CoA moiety, mediated by a set of conserved positively charged residues.

}, issn = {2041-1723}, doi = {10.1038/s41467-019-11931-1}, author = {Sathyanarayanan, Nitish and Cannone, Giuseppe and Gakhar, Lokesh and Katagihallimath, Nainesh and Sowdhamini, Ramanathan and Ramaswamy, Subramanian and Vinothkumar, Kutti R} } @article {1159, title = {Molecular mechanisms and structural features of cardiomyopathy-causing troponin T mutants in the tropomyosin overlap region.}, journal = {Proc Natl Acad Sci U S A}, volume = {114}, year = {2017}, month = {2017 10 17}, pages = {11115-11120}, abstract = {

Point mutations in genes encoding sarcomeric proteins are the leading cause of inherited primary cardiomyopathies. Among them are mutations in the gene that encodes cardiac troponin T (TnT). These mutations are clustered in the tropomyosin (Tm) binding region of TnT, TNT1 (residues 80-180). To understand the mechanistic changes caused by pathogenic mutations in the TNT1 region, six hypertrophic cardiomyopathy (HCM) and two dilated cardiomyopathy (DCM) mutants were studied by biochemical approaches. Binding assays in the absence and presence of actin revealed changes in the affinity of some, but not all, TnT mutants for Tm relative to WT TnT. HCM mutants were hypersensitive and DCM mutants were hyposensitive to Ca in regulated actomyosin ATPase activities. To gain better insight into the disease mechanism, we modeled the structure of TNT1 and its interactions with Tm. The stability predictions made by the model correlated well with the affinity changes observed in vitro of TnT mutants for Tm. The changes in Ca sensitivity showed a strong correlation with the changes in binding affinity. We suggest the primary reason by which these mutations between residues 92 and 144 cause cardiomyopathy is by changing the affinity of TnT for Tm within the TNT1 region.

}, issn = {1091-6490}, doi = {10.1073/pnas.1710354114}, author = {Gangadharan, Binnu and Sunitha, Margaret S and Mukherjee, Souhrid and Chowdhury, Ritu Roy and Haque, Farah and Sekar, Narendrakumar and Sowdhamini, Ramanathan and Spudich, James A and Mercer, John A} } @article {399, title = {Mechanistic heterogeneity in contractile properties of α-tropomyosin (TPM1) mutants associated with inherited cardiomyopathies.}, journal = {J Biol Chem}, volume = {290}, year = {2015}, month = {2015 Mar 13}, pages = {7003-15}, abstract = {

The most frequent known causes of primary cardiomyopathies are mutations in the genes encoding sarcomeric proteins. Among those are 30 single-residue mutations in TPM1, the gene encoding α-tropomyosin. We examined seven mutant tropomyosins, E62Q, D84N, I172T, L185R, S215L, D230N, and M281T, that were chosen based on their clinical severity and locations along the molecule. The goal of our study was to determine how the biochemical characteristics of each of these mutant proteins are altered, which in turn could provide a structural rationale for treatment of the cardiomyopathies they produce. Measurements of Ca(2+) sensitivity of human β-cardiac myosin ATPase activity are consistent with the hypothesis that hypertrophic cardiomyopathies are hypersensitive to Ca(2+) activation, and dilated cardiomyopathies are hyposensitive. We also report correlations between ATPase activity at maximum Ca(2+) concentrations and conformational changes in TnC measured using a fluorescent probe, which provide evidence that different substitutions perturb the structure of the regulatory complex in different ways. Moreover, we observed changes in protein stability and protein-protein interactions in these mutants. Our results suggest multiple mechanistic pathways to hypertrophic and dilated cardiomyopathies. Finally, we examined a computationally designed mutant, E181K, that is hypersensitive, confirming predictions derived from in silico structural analysis.

}, keywords = {Actins, Adenosine Triphosphatases, Calcium, Cardiomyopathies, Humans, Models, Molecular, Myosins, Point Mutation, Protein Stability, Tropomyosin}, issn = {1083-351X}, doi = {10.1074/jbc.M114.596676}, author = {Gupte, Tejas M and Haque, Farah and Gangadharan, Binnu and Sunitha, Margaret S and Mukherjee, Souhrid and Anandhan, Swetha and Rani, Deepa Selvi and Mukundan, Namita and Jambekar, Amruta and Thangaraj, Kumarasamy and Sowdhamini, Ramanathan and Sommese, Ruth F and Nag, Suman and Spudich, James A and Mercer, John A} }