New SMS mutation leads to a striking reduction in spermine synthase protein function and a severe form of Snyder-Robinson X-linked recessive mental retardation syndrome.
ABSTRACT We report the identification of a novel mutation at a highly conserved residue within the N-terminal region of spermine synthase (SMS) in a second family with Snyder-Robinson X-linked mental retardation syndrome (OMIM 309583). This missense mutation, p.G56S, greatly reduces SMS activity and leads to severe epilepsy and cognitive impairment. Our findings contribute to a better delineation and expansion of the clinical spectrum of Snyder-Robinson syndrome, support the important role of the N-terminus in the function of the SMS protein, and provide further evidence for the importance of SMS activity in the development of intellectual processing and other aspects of human development.
Article: The function of spermine[Show abstract] [Hide abstract]
ABSTRACT: Polyamines play important roles in cell physiology including effects on the structure of cellular macromolecules, gene expression, protein function, nucleic acid and protein synthesis, regulation of ion channels, and providing protection from oxidative damage. Vertebrates contain two polyamines, spermidine and spermine, as well as their precursor, the diamine putrescine. Although spermidine has an essential and unique role as the precursor of hypusine a post-translational modification of the elongation factor eIF5A, which is necessary for this protein to function in protein synthesis, no unique role for spermine has been identified unequivocally. The existence of a discrete spermine synthase enzyme that converts spermidine to spermine suggest that spermine must be needed and this is confirmed by studies with Gy mice and human patients with Snyder-Robinson syndrome in which spermine synthase is absent or greatly reduced. In both cases, this leads to a severe phenotype with multiple effects among which are intellectual disability, other neurological changes, hypotonia, and reduced growth of muscle and bone. This review describes these alterations and focuses on the roles of spermine which may contribute to these phenotypes including reducing damage due to reactive oxygen species, protection from stress, permitting correct current flow through inwardly rectifying K(+) channels, controlling activity of brain glutamate receptors involved in learning and memory, and affecting growth responses. Additional possibilities include acting as storage reservoir for maintaining appropriate levels of free spermidine and a possible non-catalytic role for spermine synthase protein. © 2014 IUBMB Life, 2014.International Union of Biochemistry and Molecular Biology Life 01/2014; 66(1). DOI:10.1002/iub.1237 · 2.76 Impact Factor
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ABSTRACT: Snyder-Robinson Syndrome (SRS) is a rare mental retardation disorder which is caused by the malfunctioning of an enzyme, the spermine synthase (SMS), which functions as a homo-dimer. The malfunctioning of SMS in SRS patients is associated with several identified missense mutations that occur away from the active site. This investigation deals with a particular SRS-causing mutation, the G56S mutation, which was shown computationally and experimentally to destabilize the SMS homo-dimer and thus to abolish SMS enzymatic activity. As a proof-of-concept, we explore the possibility to restore the enzymatic activity of the malfunctioning SMS mutant G56S by stabilizing the dimer through small molecule binding at the mutant homo-dimer interface. For this purpose, we designed an in silico protocol that couples virtual screening and a free binding energy-based approach to identify potential small-molecule binders on the destabilized G56S dimer, with the goal to stabilize it and thus to increase SMS G56S mutant activity. The protocol resulted in extensive list of plausible stabilizers, among which we selected and tested 51 compounds experimentally for their capability to increase SMS G56S mutant enzymatic activity. In silico analysis of the experimentally identified stabilizers suggested five distinctive chemical scaffolds. This investigation suggests that druggable pockets exist in the vicinity of the mutation sites at protein-protein interfaces which can be used to alter the disease-causing effects by small molecule binding. The identified chemical scaffolds are drug-like and can serve as original starting points for development of lead molecules to further rescue the disease-causing effects of the Snyder-Robinson syndrome for which no efficient treatment exists up to now.PLoS ONE 10/2014; 9(10):e110884. DOI:10.1371/journal.pone.0110884 · 3.53 Impact Factor
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ABSTRACT: The importance of mutations in disease phenotype has been studied, with information available in databases such as OMIM. However, it remains a research challenge for the possibility of clustering amino acid residues based on an underlying interaction, such as co-evolution, to understand how mutations in these related sites can lead to different disease phenotypes. This paper presents an integrative approach to identify groups of co-evolving residues, known as protein sectors. By studying a protein family using multiple sequence alignments and statistical coupling analysis, we attempted to determine if it is possible that these groups of residues could be related to disease phenotypes. After the protein sectors were identified, disease-associated residues within these groups of amino acids were mapped to a structure representing the protein family. In this study, we used the proposed pipeline to analyze two test cases of spermine synthase and Rab GDP dissociation inhibitor. The results suggest that there is a possible link between certain groups of co-evolving residues and different disease phenotypes. The pipeline described in this work could also be used to study other protein families associated with human diseases.