PSI Structural Biology Knowledgebase

PSI | Structural Biology Knowledgebase
Header Icons

Related Articles
Community-Nominated Targets
July 2015
Drug Discovery: Solving the Structure of an Anti-hypertension Drug Target
July 2015
Retrospective: 7,000 Structures Closer to Understanding Biology
July 2015
Design and Evolution: Unveiling Translocator Proteins
June 2015
Signaling with DivL
May 2015
Signaling: A Platform for Opposing Functions
May 2015
Signaling: Securing Lipid-Protein Partnership
May 2015
Dynamic DnaK
March 2015
Iron-Sulfur Cluster Biosynthesis
December 2014
Mitochondrion: Flipping for UCP2
December 2014
Mitochondrion: Setting a New TRAP1
December 2014
Power in Numbers
August 2014
Quorum Sensing: A Groovy New Component
August 2014
Quorum Sensing: E. coli Gets Involved
August 2014
iTRAQing the Ubiquitinome
July 2014
Microbiome: The Dynamics of Infection
September 2013
Protein-Nucleic Acid Interaction: A Modified SAM to Modify tRNA
July 2013
Protein-Nucleic Acid Interaction: Versatile Glutamate
July 2013
PDZ Domains
April 2013
Alpha-Catenin Connections
March 2013
Cell-Cell Interaction: A FERM Connection
March 2013
Cell-Cell Interaction: Magic Structure from Microcrystals
March 2013
Cell-Cell Interaction: Modulating Self Recognition Affinity
March 2013
Bacterial Hemophores
January 2013
Archaeal Lipids
December 2012
Membrane Proteome: Capturing Multiple Conformations
December 2012
Lethal Tendencies
October 2012
Symmetry from Asymmetry
October 2012
A signal sensing switch
September 2012
Regulatory insights
September 2012
AlkB Homologs
August 2012
Budding ensemble
August 2012
Targeting Enzyme Function with Structural Genomics
July 2012
The machines behind the spindle assembly checkpoint
June 2012
Chaperone interactions
April 2012
Pilus Assembly Protein TadZ
April 2012
Revealing the Nuclear Pore Complex
March 2012
Topping off the proteasome
March 2012
Twist to open
March 2012
Disordered Proteins
February 2012
Analyzing an allergen
January 2012
Making Lipopolysaccharide
January 2012
Pulling on loose ends
January 2012
Terminal activation
December 2011
The Perils of Protein Secretion
November 2011
Bacterial Armor
October 2011
TLR4 regulation: heads or tails?
October 2011
Ribose production on demand
September 2011
Moving some metal
August 2011
Looking for lipids
July 2011
Ribofuranosyl Binding Protein
June 2011
A molecular switch for neuronal growth
May 2011
Cell wall recycler
May 2011
Added benefits
April 2011
NMR challenges current protein hydration dogma
March 2011
Nitrile Reductase QueF
March 2011
Tip formin
March 2011
Inhibiting factor
February 2011
PASK staying active
February 2011
Tryptophanyl-tRNA Synthetase
February 2011
Regulating nitrogen assimilation
January 2011
Subtle shifts
January 2011
December 2010
Function following form
October 2010
tRNA Isopentenyltransferase MiaA
August 2010
Importance of extension for integrin
June 2010
April 2010
Alg13 Subunit of N-Acetylglucosamine Transferase
February 2010
Hemolysin BL
January 2010
December 2009
Two-component signaling
December 2009
Network coverage
November 2009
Pseudouridine Synthase TruA
November 2009
Unusual cell division
October 2009
Toxin-antitoxin VapBC-5
September 2009
Salicylic Acid Binding Protein 2
August 2009
Proofreading RNA
July 2009
Ykul structure solves bacterial signaling puzzle
July 2009
Hda and DNA Replication
June 2009
Controlling p53
May 2009
Mitotic checkpoint control
May 2009
Ribonuclease and Ribonuclease Inhibitor
April 2009
The elusive helicase
April 2009
March 2009
High-energy storage system
February 2009
A new class of bacterial E3 ubiquitination enzymes
January 2009
Poly(A) RNA recognition
January 2009
Activating BAX
December 2008
Scavenger Decapping Enzyme DcpS
November 2008
Bacteriophage Lambda cII Protein
October 2008
New metal-binding domain
October 2008
Blocking AmtB
September 2008
September 2008
Aspartate Dehydrogenase
August 2008
RNase T
July 2008
May 2008

Research Themes Cell biology

A molecular switch for neuronal growth

SBKB [doi:10.1038/sbkb.2011.17]
Featured Article - May 2011
Short description: Proteoglycans can exert opposing effects on neuronal growth by competing to control the oligomerization of a common cell surface receptor.

Model for type IIa RPTP-proteoglycan interactions and their distinct functional consequences. From Coles, C. H. et al., Science, 31 March 2011, (10.1126/science.1200840)]. Reprinted with permission from AAAS.

Type IIa receptor protein tyrosine phosphatases (RPTPs), such as RPTPσ, LAR and RPTPδ, are cell surface receptors with important functions in neuronal development, function and repair. The extracellular regions, or ectodomains, of RPTPs interact with heparan sulfate proteoglycans (HSPGs) and chondroitin sulfate proteoglycans (CSPGs) with typically opposing effects on cell function, but how these opposing effects are mediated at the molecular level has been unknown.

Reporting in Science, Coles and colleagues show that neurocan, a CSPG, reduces outgrowth of dorsal root ganglion neurons, whereas in RPTPσ−/− neurons this inhibitory effect is decreased. Conversely, glypican-2, a HSPG, strongly promotes outgrowth of wild-type, but not RPTPσ−/−, neurons. They further show that the glycosaminoglycan (GAG) chains of neurocan and glypican-2 must be involved, and that their opposing effects are mediated through a common receptor, RPTPσ. Previous mutagenesis studies suggested a shared GAG-binding site in the N-terminal Ig domain of RPTPσ, so the authors analyzed the structural basis of proteoglycan recognition.

The crystal structures of the two N-terminal Ig domains (Ig1-2) of various members of the RPTP family across different species reveal a V-shaped arrangement of Ig1 and Ig2, which is stabilized by conserved interactions. Residues of RPTPσ previously shown to mediate GAG binding lie on loops between Ig1 β-strands C-D and E-F, forming an extended positively charged surface. This region is highly conserved across family members and species, suggesting a common GAG-binding mode.

The crystal structure of human LAR Ig1-2 in complex with a synthetic heparin mimic confirms the GAG-binding site location and reveals a conformational plasticity of the C-D loop, as ligand binding triggers an outward movement of residues in the C-D loop following rupture of a salt bridge. The modified topology of the GAG-binding site maintains an overall positive charge, suggesting that the combination of basic side chains used by the GAG-binding site may vary to accommodate chemically diverse GAGs.

The dimensions of the proteoglycan-binding surface from the chicken RPTPσ Ig1-2 crystal structure suggest that GAG chains may assemble RPTPσ oligomers. Indeed, heparin fragments comprising eight or more saccharide units and heparan sulfate (which consists of 30–150 saccharide units) induce RPTPσ oligomerization. In contrast, comparable chondroitin sulfate quantities did not induce clustering of any RPTP construct tested. In addition, excess chondroitin sulfate inhibits heparan sulfate–induced RPTPσ clustering, suggesting that the HSPG:CSPG ratio and its effect on receptor clustering may influence neuronal function.

Interestingly, immunofluorescence studies show that HSPGs colocalize with RPTPs in the puncta on sensory neurons in culture, whereas CSPGs localize to the extracellular matrix. This suggests that HSPGs might act in cis on cell surface receptors, whereas CSPGs function in trans. Exogenous addition of HSPG or CSPG shifts the HSPG:CSPG ratio, thereby switching the cellular response. The authors propose a model in which high levels of HSPG promote clustering of RPTPs molecules, causing an uneven distribution of phosphatase activity on the cell surface and the formation of microdomains with high phosphotyrosine levels that would support neuronal extension. Conversely, increasing the CSPG:HSPG ratio shifts the balance away from growth-promoting RPTPσ clusters, resulting in stalled axon growth. According to this scenario, molecules able to promote RPTPσ clustering may prove useful in therapeutic strategies following neuronal injury.

Arianne Heinrichs


  1. C.H. Coles et al.
    Science (31 March 2011). doi:10.1126/science.1200840

Structural Biology Knowledgebase ISSN: 1758-1338
Funded by a grant from the National Institute of General Medical Sciences of the National Institutes of Health