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Structural Basis for Ligand Binding to the Guanidine-I Riboswitch

Structural Basis for Ligand Binding to the Guanidine- I RiboswitchThe guanidine-I riboswitch is a conserved RNA element with approximately 2,000 known examples across four phyla of bacteria. It exists upstream of nitrogen metabolism and multidrug resistance transporter genes and alters expression through the specific recognition of a free guanidinium cation. Here we report the structure of a guanidine riboswitch aptamer from Sulfobacillus acidophilus at 2.7 Å resolution. Helices P1, P1a, P1b, and P2 form a coaxial stack that acts as a scaffold for ligand binding. A previously unidentified P3 helix docks into P1a to form the guanidinium binding pocket, which is completely enclosed. Every functional group of the ligand is recognized through hydrogen bonding to guanine bases and phosphate oxygens. Guanidinium binding is further stabilized through cation-p interactions with guanine bases. This allows the riboswitch to recognize guanidinium while excluding other bacterial metabolites with a guanidino group, including the amino acid arginine.

Structure. 2017 Jan 3;25(1):195-202.
doi: 10.1016/j.str.2016.11.020.
Epub 2016 Dec 22.

© Copyright 2017 Elsevier Inc.

  Reiss CW, Xiong Y, Strobel SA.

Another SBC Highlight:

Crystal structures of the human elongation factor eEFSec suggest a non-canonical mechanism for selenocysteine incorporation
Crystal structures of the human elongation factor eEFSec suggest a non-canonical mechanism for selenocysteine incorporation.



Nat Commun. 2016 Oct 6;7:12941.
doi: 10.1038/ncomms12941.

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SBC Announcements:


19-ID Pilatus Detector


SBC has implemented a Pilatus 3 X 6M detector into the User Program at beamline 19-ID. Data collected by our users has been of outstanding quality.



19-BM Robotic sample mounter available


A robot is available for use at beamline 19-BM. The sample dewar accommodates ten Unipuck magazines; pins must be 18mm in length and use either SSRL or ALS bases. Experienced users may now request remote access to 19-BM when applying for beamtime.



SBC Staff Hosting Changes


SBC staff are now available for User Support between the hours of 8:00am and 10:pm.




ALSO: Please Be Aware...!


APS requests the Experimental Safety Approval Form (ESAF) be submitted at least seven days prior to your scheduled beamtime.


Failure to submit your ESAF in advance may result in delaying the beginning of your experiment.


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Rapid Access Beamtime Available:

SBC Beamtime Request System

The on-line SBC Beamtime Request System allows users to view available beamtime on 19-ID and 19-BM, and to submit a request for rapid beamtime allocation.

Beamtime is available to the research community via a peer reviewed proposal system; it is supported by the U.S. Department of Energy, Office of Biological and Environmental Research.

Current Beamline Statistics:

APS PDB Depositions from BioSync
SBC Sector 19 2014 2015 2016 TOTAL
PDB Depositions 263 36 261 32 133 21 4885

APS Publications Database:

Publications Total
SBC-CAT Publication List: 19-ID 1453
SBC-CAT Publication List: 19-BM 527
SBC-CAT Publication List: ALL
APS Publications Database

MCSG / APCF Announcements:


The Midwest Center for Structural Genomics (MCSG) is accepting applications for access to the MCSG User Resource.


MCSG's structure determination platform is well established, and combines technologies, robotics and expertise for gene cloning, protein production, and crystallization, as well as biochemical and biophysical characterization.


For further information, please contact Andrzej Joachimiak.


Future Meetings:


CCP4 Study Weekend 2017

January 9-11, 2017

East Midlands Conference Centre; Nottingham University, UK


61st Annual Meeting of the Biophysical Society (with new Cryo-EM Subgroup meeting)

February 11-15, 2017

New Orleans; Louisiana, USA


XXIII West Coast Protein Crystallography Workshop

March 19-22, 2017

Pacific Grove; California, USA


SBC Beamline Phone Numbers:

Phone Location Number
19-ID Beamline Control Station 630-252-9823
19-ID Beamline Cordless Phone 630-252-0569
19-ID Beamline Inside D-Hutch 630-252-1819
19-BM Beamline Control Station 630-252-9833
19-BM Beamline Cordless Phone 630-252-0568
19-BM Beamline Inside D-Hutch 630-252-1719