SecA: Difference between revisions

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[http://www.nature.com/nature/journal/v455/n7215/full/nature07335.html SecA] Crystallized complexes containing Bacillus subtilis SecA without its non-essential carboxy-terminal domain, and either Thermotoga maritima SecYE or Aquifex aeolicus SecYEG. These crystals diffracted X-rays to a maximum resolution of 6.2 Å and 7.5 Å, respectively. A higher resolution data set (4.5 Å) was obtained for a complex in which both partners were from T. maritima and the SecYEG complex was seleno-methionine (Se-Met) derivatized. All complexes were crystallized in the detergent Cymal-6 in the presence of ADP and BeFx. The structure of the complex of B. subtilis SecA and T. maritima SecYE was determined by molecular replacement with a B. subtilis SecA structure<ref name=journal2/> and served as an initial model for the other complexes. The building of a 4.5 Å resolution model of the T. maritima SecA–SecY complex was facilitated by the Se-Met positions (Supplementary Fig. 1), and by the high quality of the phases, leading to an electron density map that allowed the identification of large amino acid side chains (Fig. 1a and Supplementary Fig. 2). Model building also took into account conserved interactions between amino acids in previously determined SecA and SecY structures5<ref name=journal2/>(sequence alignments are shown in Supplementary Figs 3 and 4). The final structure was refined to Rwork and Rfree factors of 27.9% and 30.3% (Table 1), respectively, and was used for all interpretations. It comprises all residues of SecA and most residues of SecYEG. No model could be built for the periplasmic loop between TM1 and TM2a of SecY (residues 42–61), as well as for residues of some termini (SecY residues 1–7 and 424–431; SecE residues 1–9; SecG residues 1–8 and 74–76). Furthermore, there are uncertainties about the tip of the loop between TM6 and TM7 (residues 240–254). An ADP–BeF3- complex was modelled into the electron density observed in the nucleotide-binding pocket of SecA (Supplementary Fig. 5).  
[http://www.nature.com/nature/journal/v455/n7215/full/nature07335.html SecA] Crystallized complexes containing Bacillus subtilis SecA without its non-essential carboxy-terminal domain, and either Thermotoga maritima SecYE or Aquifex aeolicus SecYEG. These crystals diffracted X-rays to a maximum resolution of 6.2 Å and 7.5 Å, respectively. A higher resolution data set (4.5 Å) was obtained for a complex in which both partners were from T. maritima and the SecYEG complex was seleno-methionine (Se-Met) derivatized. All complexes were crystallized in the detergent Cymal-6 in the presence of ADP and BeFx. The structure of the complex of B. subtilis SecA and T. maritima SecYE was determined by molecular replacement with a B. subtilis SecA structure<ref name=journal2/> and served as an initial model for the other complexes. The building of a 4.5 Å resolution model of the T. maritima SecA–SecY complex was facilitated by the Se-Met positions (Supplementary Fig. 1), and by the high quality of the phases, leading to an electron density map that allowed the identification of large amino acid side chains (Fig. 1a and Supplementary Fig. 2). Model building also took into account conserved interactions between amino acids in previously determined SecA and SecY structures5<ref name=journal2/>(sequence alignments are shown in Supplementary Figs 3 and 4). The final structure was refined to Rwork and Rfree factors of 27.9% and 30.3% (Table 1), respectively, and was used for all interpretations. It comprises all residues of SecA and most residues of SecYEG. No model could be built for the periplasmic loop between TM1 and TM2a of SecY (residues 42–61), as well as for residues of some termini (SecY residues 1–7 and 424–431; SecE residues 1–9; SecG residues 1–8 and 74–76). Furthermore, there are uncertainties about the tip of the loop between TM6 and TM7 (residues 240–254). An ADP–BeF3- complex was modelled into the electron density observed in the nucleotide-binding pocket of SecA (Supplementary Fig. 5).  
   
   
'''For a figure of the SecA-SecY complex click here''' [http://www.nature.com/nature/journal/v455/n7215/images/nature07335-f1.2.jpg SecA-SecY Complex]
'''For a figure of the SecA-SecY complex click here''' [http://www.nature.com/nature/journal/v455/n7215/fig_tab/nature07335_F1.html SecA-SecY Complex]
 
a, Stereo view of a A-weighted, phase combined, NCS averaged, and B-factor sharpened 2Fo - Fc electron density map (contoured at 1). The view of the lateral gate of SecY is shown, with the C-trace of SecY in grey, SecE in red, SecG in green and SecA in blue. b, Cartoon of the complex viewed from the side. The lines indicate the membrane boundaries. c, As in b, but viewed from the cytoplasm. d, The two-helix finger of SecA inside the cytoplasmic funnel of SecY. TM2b and TM8, as well as the tip of the 6–7 loop, are shown as cartoons for clarity. Plug residues are coloured in orange. e, As in d, but shown from the back.<ref name=journal2/>


==Function==
==Function==
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