Biology subjects

Chellam, S.

Publications and source records attributed to Chellam, S..

2 recordsLinked to original sources

bioRxiv2025

Structure of bacteriophage P1 head provides insight into capsid polymorphism

The highly regulated assembly of different proteins forming mature P1 myophage capsid show a unique polymorphism where the virion population is primarily divided in brackets of two different capsid sizes. The contrasting capsids, sized 95nm (capsid_L), triangulation number (T)=13 and 68nm (capsid_S) with T=7, both in Dextro format and have the same protein forming the phage head with similar intra and inter capsomeric interactions. Comparative study of the electron density maps of the capsids reveals the presence of protein appendages DarA and Hdf below the 5-fold symmetric region inside capsid_L that anchor the phage dsDNA to the capsid-shell. Such densities are also noticed in large capsids depleted off their dsDNA but not observed in capsid_S. Deficiency of these appendages in capsid_S results in a smaller sized dsDNA packed inside capsid_S. Despite missing out on nearly 60% of the phage dsDNA virions with capsid_S has all the essential genes responsible for the formation of a fully mature thermodynamically stable virion particle with structurally identical tail and baseplate as of capsid_L. Co-existence of both stable conformation in a single lysate is a unique phenomenon in the phage community and suggest that DarA and Hdf play an important role in phage capsid morphogenesis.

biophysics↗

bioRxiv2025

Divergence of an extracellular contractile injection system infectivity elucidated by high resolution structural studies of its tail-baseplate complex

Divergence to the infectivity practice by extracellular contractile injection systems (eCISs) is displayed by myophage P1 in its lytic phase involving its baseplate receding away from the host bacterium during infection. Atomic structure of the proteins forming P1s Tail Baseplate (TB) complex, determined here, using cryo electron microscopy are employed to identify a sequence of viral events explaining this unique phenomenon. The P1 baseplate is found to be devoid of protein appendages that are necessary for anchoring it to the host bacterium. To compensate this deficiency, P1s Long Tail Fibers (LTFs) affix to the hosts exterior, straighten up imparting stability to the virion for pursuing the infection process, thereby eliciting the baseplate hub and the tail sheath to ascend away, resulting in uniform compression of the latter. Upon the maximum unkinking of LTFs, a descending corkscrew motion commences that results in the non-uniform downward compression of the tail sheath, the tail tube and baseplate needle that perforates through the hosts membrane-cytoplasm, leading to a successful phage-bacterium infection.

biophysics↗