Biomedical subjects

P E Denis

Publications and source records attributed to P E Denis.

2 recordsLinked to original sources

PubMed2000

Structural and functional differences between 3-repeat and 4-repeat tau isoforms. Implications for normal tau function and the onset of neurodegenetative disease.

Tau, MAP2, and MAP4 are members of a microtubule-associated protein (MAP) family that are each expressed as "3-repeat" and "4-repeat" isoforms. These isoforms arise from tightly controlled tissue-specific and/or developmentally regulated alternative splicing of a 31-amino acid long "inter-repeat:repeat module," raising the possibility that different MAP isoforms may possess some distinct functional capabilities. Consistent with this hypothesis, regulatory mutations in the human tau gene that disrupt the normal balance between 3-repeat and 4-repeat tau isoform expression lead to a collection of neurodegenerative diseases known as FTDP-17 (fronto-temporal dementias and Parkinsonism linked to chromosome 17), which are characterized by the formation of pathological tau filaments and neuronal cell death. Unfortunately, very little is known regarding structural and functional differences between the isoforms. In our previous analyses, we focused on 4-repeat tau structure and function. Here, we investigate 3-repeat tau, generating a series of truncations, amino acid substitutions, and internal deletions and examining the functional consequences. 3-Repeat tau possesses a "core microtubule binding domain" composed of its first two repeats and the intervening inter-repeat. This observation is in marked contrast to the widely held notion that tau possesses multiple independent tubulin-binding sites aligned in sequence along the length of the protein. In addition, we observed that the carboxyl-terminal sequences downstream of the repeat region make a strong but indirect contribution to microtubule binding activity in 3-repeat tau, which is in contrast to the negligible effect of these same sequences in 4-repeat tau. Taken together with previous work, these data suggest that 3-repeat and 4-repeat tau assume complex and distinct structures that are regulated differentially, which in turn suggests that they may possess isoform-specific functional capabilities. The relevance of isoform-specific structure and function to normal tau action and the onset of neurodegenerative disease are discussed.

Alternative Splicing↗

PubMed1997

Functional interactions between the proline-rich and repeat regions of tau enhance microtubule binding and assembly.

Tau is a neuronal microtubule-associated protein that promotes microtubule assembly, stability, and bundling in axons. Two distinct regions of tau are important for the tau-microtubule interaction, a relatively well-characterized "repeat region" in the carboxyl terminus (containing either three or four imperfect 18-amino acid repeats separated by 13- or 14-amino acid long inter-repeats) and a more centrally located, relatively poorly characterized proline-rich region. By using amino-terminal truncation analyses of tau, we have localized the microtubule binding activity of the proline-rich region to Lys215-Asn246 and identified a small sequence within this region, 215KKVAVVR221, that exerts a strong influence on microtubule binding and assembly in both three- and four-repeat tau isoforms. Site-directed mutagenesis experiments indicate that these capabilities are derived largely from Lys215/Lys216 and Arg221. In marked contrast to synthetic peptides corresponding to the repeat region, peptides corresponding to Lys215-Asn246 and Lys215-Thr222 alone possess little or no ability to promote microtubule assembly, and the peptide Lys215-Thr222 does not effectively suppress in vitro microtubule dynamics. However, combining the proline-rich region sequences (Lys215-Asn246) with their adjacent repeat region sequences within a single peptide (Lys215-Lys272) enhances microtubule assembly by 10-fold, suggesting intramolecular interactions between the proline-rich and repeat regions. Structural complexity in this region of tau also is suggested by sequential amino-terminal deletions through the proline-rich and repeat regions, which reveal an unusual pattern of loss and gain of function. Thus, these data lead to a model in which efficient microtubule binding and assembly activities by tau require intramolecular interactions between its repeat and proline-rich regions. This model, invoking structural complexity for the microtubule-bound conformation of tau, is fundamentally different from previous models of tau structure and function, which viewed tau as a simple linear array of independently acting tubulin-binding sites.

Amino Acid Sequence↗