Research article summary (published 18 Oct 2009):

Structural insights into glucan phosphatase dynamics using amide hydrogen-deuterium exchange mass spectrometry.

Full Abstract

Laforin and starch excess 4 (SEX4) are founding members of a class of phosphatases that dephosphorylate phosphoglucans. Each protein contains a carbohydrate binding module (CBM) and a dual-specificity phosphatase (DSP) domain. The gene encoding laforin is mutated in a fatal neurodegenerative disease called Lafora disease (LD). In the absence of laforin function, insoluble glucans that are hyperphosphorylated and exhibit sparse branching accumulate. It is hypothesized that these accumulations trigger the neurodegeneration and premature death of LD patients. We recently demonstrated that laforin removes phosphate from phosphoglucans and hypothesized that this function inhibits insoluble glucan accumulation. Loss of SEX4 function in plants yields a similar cellular phenotype; an excess amount of insoluble, hyperphosphorylated glucans accumulates in cells. While multiple groups have shown that these phosphatases dephosphorylate phosphoglucans, there is no structure of a glucan phosphatase and little is known about the mechanism whereby they perform this action. We utilized hydrogen-deuterium exchange mass spectrometry (DXMS) and structural modeling to probe the conformational and structural dynamics of the glucan phosphatase SEX4. We found that the enzyme does not undergo a global conformational change upon glucan binding but instead undergoes minimal rearrangement upon binding. The CBM has improved protection from deuteration when bound to glucans, confirming its role in glucan binding. More interestingly, we identified structural components of the DSP that also have improved protection from deuteration upon glucan addition. To determine the position of these regions, we generated a homology model of the SEX4 DSP. The homology model shows that all of these regions are adjacent to the DSP active site. Therefore, our results suggest that these regions of the DSP participate in the presentation of the phosphoglucan to the active site and provide the first structural analysis and mode of action of this unique class of phosphatases.

Author information

Author/s: Hsu, Simon (S); Kim, Youngjun (Y); Li, Sheng (S); Durrant, Eric S (ES); Pace, Rachel M (RM); Woods, Virgil L (VL); Gentry, Matthew S (MS);

Affiliation: Department of Medicine, University of California at San Diego, La Jolla, California 92093-0601, USA.

Grants: 5P20RR0202171 (Agency:NCRR NIH HHS) ; 5R00NS061803 (Agency:NINDS NIH HHS) ; AI068730, (Agency:NIAID NIH HHS) ; AI072106 (Agency:NIAID NIH HHS) ; AI076961 (Agency:NIAID NIH HHS) ; AI081982 (Agency:NIAID NIH HHS) ; AI2008031 (Agency:NIAID NIH HHS) ; CA099835 (Agency:NCI NIH HHS) ; CA118595 (Agency:NCI NIH HHS) ; GM020501 (Agency:NIGMS NIH HHS) ; GM037684 (Agency:NIGMS NIH HHS) ; GM066170 (Agency:NIGMS NIH HHS)

Journal and publication information

Publication Type: Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't

Journal: Biochemistry (Biochemistry), published in United States. (Language: eng)

Reference: 2009-Oct; vol 48 (issue 41) : pp 9891-902

Dates: Created 2009/10/13; Completed 2009/11/02; Revised 2009/11/05;

PMID: 19754155, status: MEDLINE (last retrieval date: 11/5/2009, IMS Date: )

Sourced from the National Library of Medicine. Abstract text and other information may be subject to copyright.

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MeSH headings (categories)

This article was linked to the MESH Headings shown below.

Amino Acid Sequence Arabidopsis - metabolism Arabidopsis Proteins - chemistry; metabolism Chromatography, Gel Deuterium Glucans - chemistry; metabolism Hydrogen

Mass Spectrometry Models, Molecular Molecular Sequence Data Peptide Fragments - chemistry Phosphoric Monoester Hydrolases - chemistry; metabolism Protein Conformation Recombinant Proteins - chemistry; metabolism

Associated Chemicals: Arabidopsis Proteins (0) ; Glucans (0) ; Peptide Fragments (0) ; Recombinant Proteins (0) ; glucan phosphate (0) ; Hydrogen (1333-74-0) ; Deuterium (7782-39-0) ; Phosphoric Monoester Hydrolases (EC 3.1.3.-)

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