Studies On The Symmetry-mismatch Structures Of Phage Lambda

Bacteriophage is a virus that infects bacteria.It has attracted much attention as a possible alternative to antibiotics in the future.At the same time,phage is often used as a model biological system to study the life cycle of virus infection,assembly,genome release and so on.Structure determines function,and the study of phage structure is of great significance for related functions and applications.Most tailed phages consist of an icosahedral symmetrical capsid enclosing double-stranded DNA and a rotating symmetrical tail,which is connected to a vertex of the icosahedral capsid via a portal protein to form a symmetrical mismatch structure.Because of the special tail structure and the large molecular weight,it is difficult for phages to grow into crystals,so cryo-electron microscopy has become the most powerful tool for analyzing the structure of phages.However,due to the limitation of the 3D reconstruction method,the existing research on phage structure mainly focuses on the icosahedral symmetrical capsid.There are relatively few symmetrical mismatched whole viral structures,especially the atomic structures.The lack of structures restricts the functional and applied studies of phages.Lambda phage has been widely studied as a model system for gene regulation,but its structure is relatively less studied.The highest resolution of the icosahedral capsid only reaches the sub-nanometer resolution of 6.8(?),and nuclear magnetic resonance(NMR)technology to parse the structure of several other protein monomer,the analysis of the symmetric mismatch structure of Lambda phage is still in the blank.This paper by phage lambda as the research object,using single particle technique of cryo-electron microscopy and research development of symmetric mismatch reconstruction method,resolved the icosahedron capsid protein and symmetric mismatch in atomic resolution(? 3.5 (?))three-dimensional structure,based on the density of refactoring to build the whole atomic structure model of the virus,explains the virus structure,function and assembly process.The main work of this project is as follows:1)Lambda phage samples with good homogeneity and high concentration were prepared,and a large number of cryo-electron microscopic images were collected.The capsid structure with a resolution of 3.7 (?) was obtained by using the icosahedron 3D reconstruction method,and the three-dimensional structure of the symmetric mismatch protein with a resolution of 3.5 (?) was obtained by using the symmetric mismatch reconstruction method.2)A full-atomic structure model of Lambda capsid was reconstructed based on icosahedral mass density,which confirmed that the N-terminal residues of gp D interacted with capsid proteins,thus stabilizing the tremendous internal pressure of the capsid during DNA packaging.By comparing the structures of capsid proteins of Lambda phage with those of HK97,BPP-1,SF6 and T4,we found the conformational changes of capsid proteins,and illustrated that the diversity of conformational changes provides significant strength and flexibility for capsid assembly and DNA packaging,thus obtaining the basis for enhancing the stability of capsid structures.3)Based on the symmetric mismatch reconstruction density,we reconstructed the full-atomic structural models of the portal protein gp B,protein gp W?head-tail junction protein gp FII?termination protein gp U and tail-tail tube protein gpV of Lambda phage,and further illustrates these symmetrical mismatch protein function and significance in virus assembly.