Limits...
Molecular characterization of abLIM, a novel actin-binding and double zinc finger protein.

Roof DJ, Hayes A, Adamian M, Chishti AH, Li T - J. Cell Biol. (1997)

Bottom Line: However, a polypeptide corresponding to the full-length isoform is found exclusively in the retina and is enriched in biochemical extracts of retinal rod inner segments. abLIM protein also undergoes extensive phosphorylation in light-adapted retinas in vivo, and its developmental expression in the retina coincides with the elaboration of photoreceptor inner and outer segments.Based on the composite primary structure of abLIM protein, actin-binding capacity, potential regulation via phosphorylation, and isoform expression pattern, we speculate that abLIM may play a general role in bridging the actin-based cytoskeleton with an array of potential LIM protein-binding partners.The developmental time course of abLIM expression in the retina suggests that the retina-specific isoform may have a specialized role in the development or elaboration of photoreceptor inner and outer segments.

View Article: PubMed Central - PubMed

Affiliation: Berman-Gund Laboratory for the Study of Retinal Degenerations, Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts 02114, USA.

ABSTRACT
Molecules that couple the actin-based cytoskeleton to intracellular signaling pathways are central to the processes of cellular morphogenesis and differentiation. We have characterized a novel protein, the actin-binding LIM (abLIM) protein, which could mediate such interactions between actin filaments and cytoplasmic targets. abLIM protein consists of a COOH-terminal cytoskeletal domain that is fused to an NH2-terminal domain consisting of four double zinc finger motifs. The cytoskeletal domain is approximately 50% identical to erythrocyte dematin, an actin-bundling protein of the red cell membrane skeleton, while the zinc finger domains conform to the LIM motif consensus sequence. In vitro expression studies demonstrate that abLIM protein can bind to F-actin through the dematin-like domain. Transcripts corresponding to three distinct isoforms have a widespread tissue distribution. However, a polypeptide corresponding to the full-length isoform is found exclusively in the retina and is enriched in biochemical extracts of retinal rod inner segments. abLIM protein also undergoes extensive phosphorylation in light-adapted retinas in vivo, and its developmental expression in the retina coincides with the elaboration of photoreceptor inner and outer segments. Based on the composite primary structure of abLIM protein, actin-binding capacity, potential regulation via phosphorylation, and isoform expression pattern, we speculate that abLIM may play a general role in bridging the actin-based cytoskeleton with an array of potential LIM protein-binding partners. The developmental time course of abLIM expression in the retina suggests that the retina-specific isoform may have a specialized role in the development or elaboration of photoreceptor inner and outer segments.

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Structure of the abLIM polypeptides. (a) Diagrams of  the protein structures of three abLIM isoforms. Features indicated in the protein sequence are: VILLIN, homology to both dematin and the villin headpiece; DEMATIN-undefined, homology  to the “undefined” domain of dematin; LIM1–4, LIM motifs. Together, the VILLIN + DEMATIN-undefined regions make up  the dematin-like region of abLIM. (b) Sequence comparison of  the four LIM domains from paxillin and abLIM protein. The  LIM consensus sequence is indicated at the bottom of the figure.  Conserved C/H/D residues within the LIM backbone are indicated by dark shading, conserved hydrophobic residues are indicated by light shading, and residues conserved only within the  four abLIM protein LIM domains are indicated by unshaded  boxes.
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Figure 4: Structure of the abLIM polypeptides. (a) Diagrams of the protein structures of three abLIM isoforms. Features indicated in the protein sequence are: VILLIN, homology to both dematin and the villin headpiece; DEMATIN-undefined, homology to the “undefined” domain of dematin; LIM1–4, LIM motifs. Together, the VILLIN + DEMATIN-undefined regions make up the dematin-like region of abLIM. (b) Sequence comparison of the four LIM domains from paxillin and abLIM protein. The LIM consensus sequence is indicated at the bottom of the figure. Conserved C/H/D residues within the LIM backbone are indicated by dark shading, conserved hydrophobic residues are indicated by light shading, and residues conserved only within the four abLIM protein LIM domains are indicated by unshaded boxes.

Mentions: The general structure of the two largest abLIM isoforms deduced from the cDNA sequences is a linear combination of two structurally and functionally distinct domains, each representing about half of the total length of the protein (Fig. 4 a). The COOH-terminal domain of abLIM-m and -l isoforms, as well as the complete sequence of abLIM-s, are ∼50% identical to dematin, an actin-bundling protein from the human erythrocyte membrane skeleton (Rana et al., 1993) (Fig. 4 a). Only a few specific functional aspects of the dematin sequence appear to be conserved in abLIM. A portion of the actin-binding region of dematin at the extreme COOH terminus (dematin amino acid residues 340–383; Rana et al., 1993) is highly conserved in the abLIM polypeptides (abLIM amino acid residues 735–778; Fig. 4 a, VILLIN). This region corresponds to a previously described sequence within the headpiece of villin (Friederich et al., 1992) that shares some homology with the product of a Drosophila villin-like gene, quail (Mahajan-Miklos et al., 1994). These sequences are thought to be directly involved in the binding of both dematin and villin to actin filaments. In contrast, most of the other key features of the dematin primary sequence are not conserved in the abLIM proteins (Rana et al., 1993). The ability of dematin to form trimers is believed to be mediated by a single essential cysteine residue at amino acid position 194 of the dematin sequence. This cysteine is not conserved in the abLIM sequence, which has no cysteine residues within the region of dematin homology. Other features of the dematin sequence that are absent from the abLIM protein primary sequence are a PEST sequence that may be involved in rapid intracellular turnover of dematin and a putative polyglutamate nuclear localization sequence.


Molecular characterization of abLIM, a novel actin-binding and double zinc finger protein.

Roof DJ, Hayes A, Adamian M, Chishti AH, Li T - J. Cell Biol. (1997)

Structure of the abLIM polypeptides. (a) Diagrams of  the protein structures of three abLIM isoforms. Features indicated in the protein sequence are: VILLIN, homology to both dematin and the villin headpiece; DEMATIN-undefined, homology  to the “undefined” domain of dematin; LIM1–4, LIM motifs. Together, the VILLIN + DEMATIN-undefined regions make up  the dematin-like region of abLIM. (b) Sequence comparison of  the four LIM domains from paxillin and abLIM protein. The  LIM consensus sequence is indicated at the bottom of the figure.  Conserved C/H/D residues within the LIM backbone are indicated by dark shading, conserved hydrophobic residues are indicated by light shading, and residues conserved only within the  four abLIM protein LIM domains are indicated by unshaded  boxes.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2141644&req=5

Figure 4: Structure of the abLIM polypeptides. (a) Diagrams of the protein structures of three abLIM isoforms. Features indicated in the protein sequence are: VILLIN, homology to both dematin and the villin headpiece; DEMATIN-undefined, homology to the “undefined” domain of dematin; LIM1–4, LIM motifs. Together, the VILLIN + DEMATIN-undefined regions make up the dematin-like region of abLIM. (b) Sequence comparison of the four LIM domains from paxillin and abLIM protein. The LIM consensus sequence is indicated at the bottom of the figure. Conserved C/H/D residues within the LIM backbone are indicated by dark shading, conserved hydrophobic residues are indicated by light shading, and residues conserved only within the four abLIM protein LIM domains are indicated by unshaded boxes.
Mentions: The general structure of the two largest abLIM isoforms deduced from the cDNA sequences is a linear combination of two structurally and functionally distinct domains, each representing about half of the total length of the protein (Fig. 4 a). The COOH-terminal domain of abLIM-m and -l isoforms, as well as the complete sequence of abLIM-s, are ∼50% identical to dematin, an actin-bundling protein from the human erythrocyte membrane skeleton (Rana et al., 1993) (Fig. 4 a). Only a few specific functional aspects of the dematin sequence appear to be conserved in abLIM. A portion of the actin-binding region of dematin at the extreme COOH terminus (dematin amino acid residues 340–383; Rana et al., 1993) is highly conserved in the abLIM polypeptides (abLIM amino acid residues 735–778; Fig. 4 a, VILLIN). This region corresponds to a previously described sequence within the headpiece of villin (Friederich et al., 1992) that shares some homology with the product of a Drosophila villin-like gene, quail (Mahajan-Miklos et al., 1994). These sequences are thought to be directly involved in the binding of both dematin and villin to actin filaments. In contrast, most of the other key features of the dematin primary sequence are not conserved in the abLIM proteins (Rana et al., 1993). The ability of dematin to form trimers is believed to be mediated by a single essential cysteine residue at amino acid position 194 of the dematin sequence. This cysteine is not conserved in the abLIM sequence, which has no cysteine residues within the region of dematin homology. Other features of the dematin sequence that are absent from the abLIM protein primary sequence are a PEST sequence that may be involved in rapid intracellular turnover of dematin and a putative polyglutamate nuclear localization sequence.

Bottom Line: However, a polypeptide corresponding to the full-length isoform is found exclusively in the retina and is enriched in biochemical extracts of retinal rod inner segments. abLIM protein also undergoes extensive phosphorylation in light-adapted retinas in vivo, and its developmental expression in the retina coincides with the elaboration of photoreceptor inner and outer segments.Based on the composite primary structure of abLIM protein, actin-binding capacity, potential regulation via phosphorylation, and isoform expression pattern, we speculate that abLIM may play a general role in bridging the actin-based cytoskeleton with an array of potential LIM protein-binding partners.The developmental time course of abLIM expression in the retina suggests that the retina-specific isoform may have a specialized role in the development or elaboration of photoreceptor inner and outer segments.

View Article: PubMed Central - PubMed

Affiliation: Berman-Gund Laboratory for the Study of Retinal Degenerations, Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts 02114, USA.

ABSTRACT
Molecules that couple the actin-based cytoskeleton to intracellular signaling pathways are central to the processes of cellular morphogenesis and differentiation. We have characterized a novel protein, the actin-binding LIM (abLIM) protein, which could mediate such interactions between actin filaments and cytoplasmic targets. abLIM protein consists of a COOH-terminal cytoskeletal domain that is fused to an NH2-terminal domain consisting of four double zinc finger motifs. The cytoskeletal domain is approximately 50% identical to erythrocyte dematin, an actin-bundling protein of the red cell membrane skeleton, while the zinc finger domains conform to the LIM motif consensus sequence. In vitro expression studies demonstrate that abLIM protein can bind to F-actin through the dematin-like domain. Transcripts corresponding to three distinct isoforms have a widespread tissue distribution. However, a polypeptide corresponding to the full-length isoform is found exclusively in the retina and is enriched in biochemical extracts of retinal rod inner segments. abLIM protein also undergoes extensive phosphorylation in light-adapted retinas in vivo, and its developmental expression in the retina coincides with the elaboration of photoreceptor inner and outer segments. Based on the composite primary structure of abLIM protein, actin-binding capacity, potential regulation via phosphorylation, and isoform expression pattern, we speculate that abLIM may play a general role in bridging the actin-based cytoskeleton with an array of potential LIM protein-binding partners. The developmental time course of abLIM expression in the retina suggests that the retina-specific isoform may have a specialized role in the development or elaboration of photoreceptor inner and outer segments.

Show MeSH