Glut-1 as a receptor for htlv envelopes and its uses

Abstract

The present application relates to a method for diagnosing a glucose transporter type 1 (GLUT1) deficiency syndrome that utilizes polypeptides derived from the soluble part of the glycoprotein of the enveloped virus of primate T-cell leukemia virus (PTLV). The polypeptides, named receptor binding domain ligands (RBD), are selected for their ability to bind specifically to GLUT1. The method involves determining the level of GLUT 1 expression at the cell surface and comparing the level to a reference value.

1 . A method for diagnosing a glucose transporter type 1 (GLUT1) deficiency syndrome, comprising:
 a) collecting sample from a subject,   b) determining the level of GLUT1 expression at a cell surface using an isolated polypeptide, wherein said polypeptide is a soluble receptor binding domain (RBD) ligand derived from the soluble part of the glycoprotein of a primate T-lymphotropic virus binding to GLUT1 or a fragment thereof, and   c) comparing said level to a reference value.   
     
     
         2 . The method of  claim 1 , wherein GLUT1 comprises an amino acid sequence presenting a sequence identity of at least 70% with SEQ ID NO: 2. 
     
     
         3 . The method of  claim 1 , wherein the RBD ligand binds to at least one of the following fragments of GLUT1: 
       
         
           
                 
                 
               
                     
                   SEQ ID NO: 42 
                 
                     
                   (IVGMCFQYVEQLC) 
                 
                     
                     
                 
                     
                   SEQ ID NO: 35 
                 
                     
                   (NAPQKVIEEFY) 
                 
                     
                     
                 
                     
                   SEQ ID NO: 36 
                 
                     
                   (NQTWVHRYGESILPTTLTTLWS) 
                 
                     
                     
                 
                     
                   SEQ ID NO: 37 
                 
                     
                   (KSFEMLILGR) 
                 
                     
                     
                 
                     
                   SEQ ID NO: 38 
                 
                     
                   (DSIMGNKDL) 
                 
                     
                     
                 
                     
                   SEQ ID NO: 39 
                 
                     
                   (YSTSIFEKAGVQQP) 
                 
                     
                     
                 
                     
                   SEQ ID NO: 40 
                 
                     
                   (EQLPWMSYLS) 
                 
                     
                     
                 
                     
                   SEQ ID NO: 41 
                 
                     
                   (QYVEQLC) 
                 
             
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
     
     
         4 . The method of  claim 1 , wherein the RBD ligand is selected from the group consisting of human T-cell leukemia virus (HTLV) 2.RBD, HTLV1.RBD, HTLV4.RBD, HTLV3.RBD, simian T-cell leukemia virus (STLV) 1.RBD, STLV2.RBD and STLV3.RBD. 
     
     
         5 . The method of  claim 4 , wherein HTLV2.RBD comprises the amino acid sequence SEQ ID NO: 4 or SEQ ID NO: 5 or SEQ ID NO: 7 or SEQ ID NO: 43 or fragments or variants thereof. 
     
     
         6 . The method of  claim 4 , wherein HTLV1.RBD comprises the amino acid sequence SEQ ID NO: 9 or SEQ ID NO: 10 or SEQ ID NO: 11 or SEQ ID NO: 13 or SEQ ID NO: 15 or SEQ ID NO: 17 or SEQ ID NO: 19 or SEQ ID NO: 21 or fragments or variants thereof. 
     
     
         7 . The method of  claim 4 , wherein HTLV4.RBD comprises the amino acid sequence SEQ ID NO: 22 or SEQ ID NO: 23 or SEQ ID NO: 51 or fragments or variants thereof. 
     
     
         8 . The method of  claim 4 , wherein HTLV3.RBD comprises the amino acid sequence SEQ ID NO: 53 or fragments or variants thereof. 
     
     
         9 . The method of  claim 4 , wherein STLV1.RBD comprises the amino acid sequence SEQ ID NO: 25 or fragments or variants thereof. 
     
     
         10 . The method of  claim 4 , wherein STLV2.RBD comprises the amino acid sequence SEQ ID NO: 27 or fragments or variants thereof. 
     
     
         11 . The method of  claim 4 , wherein STLV3.RBD comprises the amino acid sequence SEQ ID NO: 29 or SEQ ID NO: 55 or fragments or variants thereof. 
     
     
         12 . The method of  claim 1 , wherein the RBD ligand is fused to a tag, an antibody constant fragment or a fluorescent protein. 
     
     
         13 . The method of  claim 1 , wherein the reference value consists of the level of GLUT1 expression at the cell surface determined in a sample from a substantially healthy subject. 
     
     
         14 . The method of  claim 1 , wherein the reference value consists of the level of GLUT1 expression at the cell surface determined in samples from a reference population comprising at least 100 substantially healthy subjects. 
     
     
         15 . The method of  claim 1 , wherein the reference value consists of the level of GLUT1 expression at the cell surface determined in a sample from a subject having a GLUT1 deficiency syndrome. 
     
     
         16 . The method of  claim 1 , wherein the reference value consists of the level of GLUT1 expression at the cell surface determined in samples from a reference population comprising at least 10 subjects having a GLUT1 deficiency syndrome. 
     
     
         17 . The method of  claim 1 , wherein the GLUT1 deficiency syndrome is characterized by an encephalopathy marked by childhood epilepsy that is refractory to treatment, deceleration of cranial growth leading to microcephaly, psychomotor retardation, spasticity, ataxia, dysarthria or other paroxysmal neurological phenomena often occurring before meals. 
     
     
         18 . The method of  claim 1 , wherein the GLUT1 deficiency syndrome is associated with de novo or inherited mutations in the SLC2A1 gene. 
     
     
         19 . The method of  claim 1 , wherein the GLUT1 deficiency syndrome is associated with low glucose level and low lactate concentration in the cerebrospinal fluid (CSF) in the absence of hypoglycemia.