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statement: 23 Actin cross-linking (ACD) domain of VgrG-1 toxin of Type VI secretion in Vibrio cholera has 24 WASP Homology domain 2 (WH2) domain. ACD interact with actin through WH2 domain, 25 WH2 is essential for ACD mediated cross-linking and disruption of actin cytoskeleton in the host 26 cell. 27 28 Abstract: 29 Type VI secretion systems (T6SS) plays a crucial role in Vibrio cholerae mediated pathogenicity 30 and predation. Tip of T6SS is homologous to gp27/gp5 complex or tail spike of T4 31 bacteriophage. VgrG-1 of V. cholerae T6SS is unusual among other VgrG because its effector 32 domain is trans-located into the cytosol of eukaryotic cells with an additional actin cross-linking 33 domain (ACD) at its C terminal end. ACD of VgrG-1 (VgrG-1-ACD) causes T6SS dependent 34 host cell cytotoxicity through actin cytoskeleton disruption to prevent bacterial engulfment by 35 macrophages. ACD mediated actin cross-linking promotes survival of the bacteria in the small 36 intestine of humans, along with other virulence factors; establishes successful infection with the 37 onset of diarrhoea in humans. Our studies demonstrated VgrG-1-ACD can bind to actin besides 38 actin cross-linking activity. Computational analysis of ACD revealed the presence of WH2 39 domain through which it binds actin. Mutations in WH2 domain lead to loss of actin binding in 40 vitro. VgrG-1-ACD having the mutated WH2 domain cannot cross-link actin efficiently in vitro 41 and manifests less actin cytoskeleton disruption when transfected in HeLa cells.42 43 Introduction: 44 Cholera is life threatening water borne diarrheal disease caused by the gram negative bacterium 45 Vibrio cholerae. The O1 and O139 V. cholerae serogroups produce primarily an enterotoxin 46 called the CTX or cholera toxin. Cholera toxin is the main cause of diarrhoea [1, 2 and 3]. Other 47 accessory toxins from V. cholerae including hemaglutinin/protease (hapA) or hemolysin (hlyA), 48 zot, Ace, VgrG-1, VopF/L are also involved in the pathogenesis [4 and 5]. Among these, 49 Multifunctional Autoprocessing Repeats-in-Toxins (MARTX) and VgrG (Valine-Glycine Repeat 50 Protein G) toxins are important categories of toxins having a signature Actin Cross-linking 51 Domain (ACD) [6]. Type VI secretion systems (T6SS) is known to secrete three related proteins-52 VgrG-1, VgrG-2 and VgrG-3. VgrG components of the T6SS apparatus are capable to assemble 53 and form a drilling device analogous to tail spikes in phages [7]. VgrG has similar structure 54 resembling gp27/gp5 complex or the tail spike of T4 bacteriophage with an additional actin 55 cross-linking domain at its C-terminal end that covalently cross-links the globular actin, leading 56 to disruption of the host intrinsic actin cytoskeleton arrangements and cause rounded cell 57 morphology [8 and 9]. The VgrG-1 of V. cholerae (T6SS) is unique compared to other VgrG, 58 because its ACD containing effector domain is trans-located into the cytosol of eukaryotic cells 59[10]. In short, VgrG-1 helps Vibrio to prevent amoebic predation, ...

The coordinated contraction of myocytes drives the heart to beat and circulate blood. Due to the limited spatial resolution of whole heart imaging and the piecemeal nature of high-magnification studies, a confirmed model of myofiber geometry does not yet exist. Using microscopy and computer vision we report the first three-dimensional reconstruction of myofibers across entire mouse ventricular walls at the micron scale, representing a gain of three orders of magnitude in spatial resolution over the existing models. Our analysis reveals prominent longitudinal bands of fibers that are orthogonal to the well-known circumferential ones. Our discovery impacts present understanding of heart wall mechanics and electrical function, with fundamental implications for the study of diseases related to myofiber disorganization.