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Biochemistry Seminar – Dr. Petr Leiman:”Function, structure, and evolution of phage spike tip proteins”
October 23, 2019 @ 4:00 pm - 5:00 pm
Dr. Petr Leiman
Department of Biochemistry and Molecular Biology
Sealy Center for Structural Biology and Molecular Biophysics
University of Texas Medical Branch, Galveston
Title: “Function, structure, and evolution of phage spike tip proteins”
Abstract:The process of protein and DNA translocation across lipid membranes is central to the function of any organism. Contractile injection systems, which include bacteriophage tails, Type VI Secretion System, R-type pyocins, Photorhabdus Virulence Cassette, Serratia antifeeding prophage, and others, translocate their substrates using a rigid tube/contractile sheath mechanism. Functionally and structurally, these systems resemble a stretched spring (or sheath) wound around a non-contractile tube, which carries a spike-shaped complex at its membrane-proximal end. The complex consists of three modules – a hub, a central spike, and a spike’s tip – that can be encoded by separate genes or fused together. The spike tip forms the membrane-attacking component of the complex. In this talk, we will examine the structure, evolution, and function of spike tip proteins. In particular, I will present data that demonstrate that 1) phage T4 spike tip protein gp5.4 is dispensable for particle assembly but essential for its fitness and infection efficiency; and 2) phage P2 spike gpV is translocated through the outer membrane into the periplasm upon sheath contraction. We will also examine crystal structures of central spikes and central spike tip proteins of phages T4, SN, PhiKZ, and OBP, as well as that of the Photorhabdus Virulence Cassette, and the fit of these complexes into cryo-electron microscopy (cryoEM) reconstructions of these organelles. We also examine a cryoEM reconstruction of the T4-like phage RB43 tail that carries an uncommon tip protein. These findings demonstrate conservation of core features as well as host-adapted diversity of spike and tip proteins and show that spike tip proteins are critically important for efficient membrane-penetrating function by contractile tail-like systems.
Host: Lanying Zeng
Biochemistry Building (Bldg.#1507)