Mice that are homozygous for the autosomal recessive chondrodysplasia (cho) mutation die at birth with abnormalities in cartilage of limbs, ribs, mandible, and trachea. Limb bones of newborn cho/cho mice are wider at the metaphyses than normal bones and only about half the normal length. By linkage analysis, the cho gene and the gene encoding the alpha 1 (XI) chain of cartilage collagen XI were mapped to the same region of chromosome 3. Deletion of a cytidine residue about 570 nt downstream of the translation initiation codon in cho alpha 1 (XI) mRNA causes a reading frame shift and introduces a premature stop codon. The data demonstrate that collagen XI is essential for normal formation of cartilage collagen fibrils and the cohesive properties of cartilage. The results also suggest that the normal differentiation and spatial organization of growth plate chondrocytes is critially dependent on the presence of type XI collagen in cartilage extracellular matrix.

Protein aggregation is a hallmark of several neurodegenerative diseases and also of cataracts. The major proteins in the lens of the eye are crystallins, which accumulate throughout life and are extensively modified. Deamidation is the major modification in the lens during aging and cataracts. Among the crystallins, the bA3-subunit has been found to have multiple sites of deamidation associated with the insoluble proteins in vivo. Several sites were predicted to be exposed on the surface of bA3 and were investigated in this study. Deamidation was mimicked by site-directed mutagenesis at Q42 and N54 on the N-terminal domain, N133 and N155 on the C-terminal domain, and N120 in the peptide connecting the domains. Deamidation altered the tertiary structure without disrupting the secondary structure or the dimer formation of bA3. Deamidations in the C-terminal domain and in the connecting peptide decreased stability to a greater extent than deamidations in the N-terminal domain. Deamidation at N54 and N155 also disrupted the association with the bB1-subunit. Sedimentation velocity experiments integrated with high-resolution analysis detected soluble aggregates at 15%-20% in all deamidated proteins, but not in wild-type bA3. These aggregates had elevated frictional ratios, suggesting that they were elongated. The detection of aggregates in vitro strongly suggests that deamidation may contribute to protein aggregation in the lens. A potential mechanism may include decreased stability and/or altered interactions with other b-subunits. Understanding the role of deamidation in the long-lived crystallins has important implications in other aggregation diseases.Keywords: lens; bA3-crystallin; deamidation; protein aggregation; cataract; sedimentation velocity Cataract is the most common cause of preventable blindness in the world (Resnikoff et al. 2004). Age-related cataract is a protein aggregation disease associated with the insolubization of modified proteins in the lens (Harrington et al. 2004). The lens contains a high concentration of proteins that are mostly structural proteins called crystallins. To enable transparency, crystallins form hetero-oligomers that assemble into ordered structures (Delaye and Tardieu 1983). Modifications that disrupt this order most likely contribute to aggregation and precipitation.The proteins from older lenses contain many modifications including truncation, methylation, oxidation, disulfide bond formation, glycation, racemization, and deamidation (Groenen et

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DICER1 syndrome is a rare genetic disorder that predisposes individuals to multiple cancer types. Through mutations of the gene encoding the endoribonuclease, Dicer, DICER1 syndrome disrupts the biogenesis and processing of miRNAs with subsequent disruption in control of gene expression. Since the first description of DICER1 syndrome, case reports have documented novel germline mutations of the DICER1 gene in patients with cancers as well as second site mutations that alter the function of the Dicer protein expressed. Here, we present a review of mutations in the DICER1 gene, the respective protein sequence changes, and clinical manifestations of DICER1 syndrome. Directions for future research are discussed.

Parkinson's disease (PD) and dementia with Lewy bodies (DLB) are both characterized pathologically by the presence of neuronal inclusions termed Lewy bodies (LBs). A common feature found in LBs are aggregates of alpha-synuclein (alpha-Syn), and although it is now recognized that alpha-Syn is the major building block for these toxic filaments, the mechanism of how this occurs remains unknown. In the present study, we demonstrate that proteolytic processing of alpha-Syn by the protease calpain I leads to the formation of aggregated high-molecular weight species and adoption of a beta-sheet structure. To determine whether calpain-cleavage of alpha-Syn occurs in PD and DLB, we designed site-directed calpain-cleavage antibodies to alpha-Syn and tested their utility in several animal model systems. Detection of calpain-cleaved alpha-Syn was evident in mouse models of cerebral ischemia and PD and in a Drosophila model of PD. In the human PD and DLB brain, calpain-cleaved alpha-Syn antibodies immunolabeled LBs and neurites in the substantia nigra. Moreover, calpain-cleaved alpha-Syn fragments identified within LBs colocalized with activated calpain in neurons of the PD and DLB brains. These findings suggest that calpain I may participate in the disease-linked aggregation of alpha-Syn in various alpha-synucleinopathies.

According to the World Health Organization, cataracts account for half of the blindness in the world, with the majority occurring in developing countries. A cataract is a clouding of the lens of the eye due to light scattering of precipitated lens proteins or aberrant cellular debris. The major proteins in the lens are crystallins and they are extensively deamidated during aging and cataracts. Deamidation has been detected at the domain and monomer interfaces of several crystallins during aging.The purpose of this study was to determine the effects of two potential deamidation sites at the predicted interface of the βA3-crystallin dimer on its structure and stability. The glutamine residues at the reported in vivo deamidation sites of Q180 in the C-terminal domain and at the homologous site Q85 in the N-terminal domain were substituted with glutamic acid residues by site-directed mutagenesis. Far UV and near UV circular dichroism spectroscopy indicated that there were subtle differences in the secondary structure and more notable differences in the tertiary structure of the mutant proteins compared to wild type βA3-crystallin. The Q85E/Q180E mutant also was more susceptible to enzymatic digestion, suggesting increased solvent accessibility. These structural changes in the deamidated mutants led to decreased stability during unfolding in urea and increased precipitation during heat-denaturation. When simulating deamidation at both residues, there was a further decrease in stability and loss of cooperativity. However, multiangle-light scattering and quasielastic light scattering experiments showed that dimer formation was not disrupted, nor did higherorder oligomers form. These results suggest that introducing charges at the predicted domain interface in the βA3 homodimer may contribute to the insolubilization of lens crystallins or favor other, more stable, crystallin subunit interactions.Cataracts account for half of all blindness according to the World Health Organization (1). The greatest incidence is in developing countries. A cataract is opacity within the lens of the eye due to scattering of light by precipitated proteins or by aberrant cellular debris. The major proteins within the lens belong to the α and β/γ-crystallin families. Protein concentrations can reach 400 mg/mL and above in the center of the lens, and it is their ordered packing that is necessary for transparency (2). There is an extremely low rate of turnover of crystallins in differentiated lens cells. Thus, crystallins accumulate modifications due to environmental and metabolic damage during an individual's entire lifetime. This makes the lens an easily accessible tissue to study the effects of post-translational modifications on protein unfolding and aggregation.The major post-translational modifications in lenses are truncation, methylation, oxidation, disulfide bond formation, advanced glycation end-products and deamidation (3)(4)(5)(6)(7)(8)(9)(10)(11)(12). Of these AUTHOR EMAIL ADDRESS lampik@ohsu.edu. NIH Public Access Author M...

Type XI collagen is an integral, although minor component of cartilage collagen fibrils. We have established that alternative exon usage is a mechanism for increasing structural diversity within the amino-terminal nontriple helical domain of the pro-alpha 1(XI) collagen gene. cDNA clones spanning the amino-terminal domain were selected from a rat chondrosarcoma library, and were shown to contain two major sequence differences from the previously reported human sequence. The first difference was the replacement of sequence encoding an acidic domain of 39 amino acids in length by a sequence encoding a 51-amino acid basic domain with a predicted pI of 11.9. The second difference was the absence of a sequence that would translate into a highly acidic 85-amino acid sequence downstream from the first variation. These two changes, expressed together, result in the replacement of most of the acidic domain with one that is smaller and basic. These two sequence differences serve to identify subdomains of a variable region, designated V1 and V2, respectively. V1a is defined as the acidic 39-amino acid sequence element and V1b is defined as the 51-amino acid basic sequence. Analysis of genomic DNA revealed that both V1a and V1b are encoded by separate adjacent exons in the rat genome and V2 is also encoded in a single exon downstream. Analysis of mRNA from cartilage-derived sources revealed a complex pattern of alpha 1(XI) transcript expression due to differential exon usage. In non-cartilage sources, the pattern is less complex; the most prevalent form is the one containing the two acidic sequences, V1a and V2.

Collagen XI is a heterotrimeric molecule found predominantly in heterotypic cartilage fibrils, where it is involved in the regulation of fibrillogenesis. This function is thought to involve the complex N-terminal domain. The goal of this current study was to examine its structural organization to further elucidate the regulatory mechanism. The amino-propeptide (␣1-Npp) alone or with isoforms of the variable region were recombinantly expressed and purified by affinity and molecular sieve chromatography. Cys-1-Cys-4 and Cys-2-Cys-3 disulfide bonds were detected by liquid chromatographytandem mass spectrometry. This pattern is identical to the homologous ␣2-Npp, indicating that the recombinant proteins were folded correctly. Anomalous elution on molecular sieve chromatography suggested that the variable region was extended, which was confirmed using rotary shadowing; the ␣1-Npp formed a globular "head" and the variable region an extended "tail." Circular dichroism spectra analysis determined that the ␣1-Npp comprised 33% ␤-sheet, whereas the variable region largely comprised non-periodic structure. Taken together, these results imply that the ␣1-Npp cannot be accommodated within the core of the fibril and that the variable region and/or minor helix facilitates its exclusion to the fibril surface. This provides further support for regulation of fibril diameter by steric hindrance or by interactions with other matrix components that affect fibrillogenesis.Collagen XI is a component of fibrils both in cartilage and a wide variety of non-cartilaginous tissues, including brain, muscle, tendon, heart valve, skin, calvaria, and endochondral bone (1, 2). In cartilage it assembles with collagens II and IX to produce an extensive network of thin, heterotypic collagen fibrils (15-25 nm in diameter; Ref. 1) in which the other extracellular matrix components are embedded. The major triple helix of collagen XI is not accessible to antibodies unless the fibrils are disrupted, which led to the model that it is located in the interior of the fibril (1, 3). In non-cartilaginous tissues, collagen XI has been found to co-assemble with chains of the highly homologous type V collagen (4, 5).Collagen XI is a heterotrimeric molecule consisting of ␣1, ␣2, and ␣3 collagen chains (6). The ␣3(XI) chain is an overglycosylated form of the ␣1(II) collagen chain (7), whereas the ␣1(XI) and ␣2(XI) chains are distinct gene products (8). The ␣1(XI) and ␣2(XI) chains contain similar large, N-terminal domains (NTDs), 1 comprising a "PARP" or "PARP-like" domain, a variable region, and a minor triple helix ( Fig. 1a; Refs. 9 and 10). The PARP (proline-arginine rich protein) domain was originally isolated as a distinct protein from bovine cartilage (11) but was later demonstrated to be a fragment of the N terminus of the ␣2(XI) chain (12). Recently, the proteolytic processing site of the ␣1(XI) chain has been identified (13,14), and since nearly all of the domain is removed by this processing event, both the PARP-like and PARP domains are now termed the ...