PDZ motifs are modular protein–protein interaction domains, consisting of 80–120 amino acid residues, whose function appears to be the direction of intracellular proteins to multiprotein complexes. In skeletal muscle, there are a few known PDZ-domain proteins, which include neuronal nitric oxide synthase and syntrophin, both of which are components of the dystrophin complex, and actinin-associated LIM protein, which binds to the spectrin-like repeats of α-actinin-2. Here, we report the identification and characterization of a new skeletal muscle protein containing a PDZ domain that binds to the COOH-terminal region of α-actinin-2. This novel 31-kD protein is specifically expressed in heart and skeletal muscle. Using antibodies produced to a fragment of the protein, we can show its location in the sarcomere at the level of the Z-band by immunoelectron microscopy. At least two proteins, 32 kD and 78 kD, can be detected by Western blot analysis of both heart and skeletal muscle, suggesting the existence of alternative forms of the protein. In fact, several forms were found that appear to be the result of alternative splicing. The transcript coding for this Z-band alternatively spliced PDZ motif (ZASP) protein maps on chromosome 10q22.3-10q23.2, near the locus for infantile-onset spinocerebellar ataxia.

Autosomal dominant lateral temporal epilepsy (EPT; OMIM 600512) is a form of epilepsy characterized by partial seizures, usually preceded by auditory signs. The gene for this disorder has been mapped by linkage studies to chromosomal region 10q24. Here we show that mutations in the LGI1 gene segregate with EPT in two families affected by this disorder. Both mutations introduce premature stop codons and thus prevent the production of the full-length protein from the affected allele. By immunohistochemical studies, we demonstrate that the LGI1 protein, which contains several leucine-rich repeats, is expressed ubiquitously in the neuronal cell compartment of the brain. Moreover, we provide evidence for genetic heterogeneity within this disorder, since several other families with a phenotype consistent with this type of epilepsy lack mutations in the LGI1 gene.

In multicellular organisms, secreted. proteins play pivotal regulatory roles in intercellular communication. Proteins secreted by skeletal muscle can act locally on muscle cells through autocrine/paracrine loops and on surrounding tissues such as muscle blood vessels, or they can be released into the blood stream, thus producing systemic effects. By a computational approach, we have screened 6255 products of genes expressed in normal human skeletal muscle. Putatively secreted proteins were identified by sequential steps of sieving, through prediction of signal peptide, recognition of transmembrane regions, and analysis of protein annotation. The resulting putative skeletal muscle secretome consists of 319 proteins, including 78 still uncharacterized proteins. This is the first human skeletal muscle secretome produced by computational analysis. Knowledge of proteins secreted by skeletal muscle could stimulate development of novel treatments for different diseases, including muscle atrophy and dystrophy. In addition, better knowledge of the secretion process in skeletal muscle can be useful for future gene therapy approaches

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