Functions of a hemolysin-like protein in the cyanobacterium Synechocystis sp. PCC 6803
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ORIGINAL PAPER
Functions of a hemolysin-like protein in the cyanobacterium Synechocystis sp. PCC 6803 Tetsushi Sakiyama · Hiroya Araie · Iwane Suzuki · Yoshihiro Shiraiwa
Received: 10 February 2011 / Accepted: 23 March 2011 / Published online: 8 April 2011 © Springer-Verlag 2011
Abstract A glucose-tolerant strain of the cyanobacterium Synechocystis sp. PCC 6803, generally referred to as wild type, produces a hemolysin-like protein (HLP) located on the cell surface. To analyze the function of HLP, we constructed a mutant in which the hlp gene was disrupted. The growth rate of the mutant was reduced when the cells were stressed by treatment with CuSO4, CdCl2, ZnCl2, ampicillin, kanamycin, or sorbitol in liquid medium, suggesting that HLP may increase cellular resistance to the inhibitory eVects of these compounds. Uptake assays with 109Cd2+ using the silicone–oil layer centrifugation technique revealed that both wild type and mutant cells were labeled with 109Cd2+ within 1 min. Although the total radioactivity was much higher in the wild-type cells, 109Cd2+ incorporation was clearly much higher in the mutant cells after adsorbed 109Cd2+ was removed from the cell surface by washing with EDTA. These Wndings suggest that HLP functions as a barrier against the adsorption of toxic compounds. Keywords Cell wall · Heavy metal stress · Hemolysinlike protein · S-layer · Cyanobacterium
Communicated by ErkoStackebrandt. Electronic supplementary material The online version of this article (doi:10.1007/s00203-011-0700-2) contains supplementary material, which is available to authorized users. T. Sakiyama · H. Araie · I. Suzuki · Y. Shiraiwa (&) Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8572, Japan e-mail: [email protected]
Introduction Bacterial cells may be surrounded by a capsule composed primarily of carbohydrate polymers or by a protein surface layer (S-layer), or both (Sleytr and Messner 2000). The crystalline S-layer is the outermost cell envelope component in many bacteria and archaea. Generally, the S-layer comprises a single protein or glycoprotein and completely covers the cell surface at all stages of bacterial growth. Ranging in thickness from 5 to 25 nm, S-layers have a lattice structure exhibiting identically sized pores with diameters of 2–8 nm. S-layer proteins, ranging in apparent molecular mass from 40 to 200 kDa, are among the most abundant cellular proteins (Sleytr and Messner 2000). The middle and C-terminal regions of S-layer proteins show low sequence identity. S-layers are reported to provide prokaryotic cells with a selective advantage by functioning as a protective coating, in cell adhesion, for surface recognition, and as ion traps. Repeat-in-toxin (RTX) proteins are exotoxins produced by Gram-negative bacteria (Ludwig 1996). RTX proteins are considered to form pores in the cytoplasmic membranes of erythrocytes, leukocytes, and other cells, leading to the modiWcation of cellular functions and/or lysis of host cells. RTX proteins ar
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