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Structural and functional analysis of the β‐barrel domain of BamA from Escherichia coli
Author(s) -
Ni Dongchun,
Wang Yan,
Yang Xu,
Zhou Haizhen,
Hou Xiaomin,
Cao Baohua,
Lu Zhixin,
Zhao Xinsheng,
Yang Kun,
Huang Yihua
Publication year - 2014
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fj.13-248450
Subject(s) - bama , biogenesis , bacterial outer membrane , transmembrane domain , transmembrane protein , barrel (horology) , escherichia coli , salt bridge , structural motif , chemistry , crystallography , mutagenesis , biophysics , protein structure , biology , mutant , membrane , biochemistry , materials science , receptor , gene , composite material
In gram‐negative bacteria, the assembly of outer membrane proteins (OMPs) requires a β‐barrel assembly machinery (BAM) complex, of which BamA is an essential and evolutionarily conserved component. To elucidate the mechanism of BamA‐mediated OMP biogenesis, we determined the crystal structure of the C‐terminal transmembrane domain of BamA from Escherichia coli ( Ec BamA) at 2.6 Å resolution. The structure reveals 2 distinct features. First, a portion of the extracellular side of the β barrel is composed of 5 markedly short β strands, and the loops stemming from these β strands form a potential surface cavity, filled by a portion of the L6 loop that includes the conserved VRGF/Y motif found in the Omp85 family. Second, the 4 extracellular loops L3, L4, L6, and L7 of Ec BamA form a dome over the barrel, stabilized by a salt‐bridge interaction network. Functional data show that hydrophilic‐to‐hydrophobic mutations of the potential hydrophilic surface cavity and a single Arg547Ala point mutation that may destabilize the dome severely affect the function of Ec BamA. Our structure of the Ec BamA β barrel and structure‐based mutagenesis studies suggest that the transmembrane β strands of OMP substrates may integrate into the outer membrane at the interface of the first and last β strands of the Ec BamA barrel, whereas the soluble loops or domains may be transported out of the cell via the hydrophilic surface cavity on dislocation of the VRGF/Y motif of L6. In addition, the dome over the barrel may play an important role in maintaining the efficiency of OMP biogenesis.—Ni, D., Wang, Y., Yang, X., Zhou, H., Hou, X., Cao, B., Lu, Z., Zhao, X., Yang, K., Huang, Y. Structural and functional analysis of the β‐barrel domain of BamA from Escherichia coli . FASEB J . 28, 2677–2685 (2014). www.fasebj.org