Procollagen alpha2 mRNA is significantly different from procollagen alpha1(I) mRNA in size or secondary structure

How electrostatic networks modulate specificity and stability of collagen

One-quarter of the 28 types of natural collagen exist as heterotrimers. The oligomerization state of collagen affects the structure and mechanics of the extracellular matrix, providing essential cues to modulate biological and pathological processes. A lack of high-resolution structural information limits our mechanistic understanding of collagen heterospecific self-assembly. Here, the 1.77-Å resolution structure of a synthetic heterotrimer demonstrates the balance of intermolecular electrostatics and hydrogen bonding that affects collagen stability and heterospecificity of assembly. Atomistic simulations and mutagenesis based on the solved structure are used to explore the contributions of specific interactions to energetics. A predictive model of collagen stability and specificity is developed for engineering novel collagen structures.

Cell-free translation products of basement membrane RNA from the EHS tumor

The biosynthetic products of the Engelbreth-Holm-Swarm (EHS) tumor and the cell-free translation products of EHS tumor cell RNA were characterized. Six distinct gene products (three laminin polypeptides, entactin/nidogen, and two collagen IV chains) comprising the basement membrane matrix were identified by a combination of proteolytic digestion and immunologic techniques. Analysis of the cell-free translation products using EHS tumor RNA precipitated by anti-laminin serum confirms earlier evidence that there are at least two B chains encoded by different genes. The anti-laminin serum also recognized entactin/nidogen, which was further identified by specific immunoprecipitation with anti-entactin serum. Radiolabeled laminin A chains, synthesized by the EHS tumor in organ culture, were also identified by the anti-laminin serum but were not detected among the cell-free translation products of EHS tumor RNA. Pulse-chase studies of EHS tumor in organ culture as well as in vitro translation of EHS tumor RNA suggest that the precursor forms of alpha 1(IV) and alpha 2(IV) collagen chains are nearly identical in size, with apparent molecular weights of 170,000. The mRNAs encoding these two polypeptides migrate differently on sucrose gradients. It is likely that glycosylation and hydroxylation of collagen IV account for the major differences in molecular weight of mature alpha 1(IV) and alpha 2(IV) chains in the EHS tumor matrix.

Construction and characterization of cDNA clones encoding the 5' end of the chicken pro alpha 1(I) collagen mRNA

As a first step in isolating the 5' end of the chicken pro alpha 1(I) collagen gene, we constructed cDNA clones complementary to the 5' end of the pro alpha 1(I) mRNA using synthetic oligodeoxynucleotides complementary to a conserved region within the N-terminal telopeptide as primers. cDNA clones corresponding to the 5'-untranslated region, signal peptide, N-propeptide and telopeptide were identified based on homology with the human pro alpha 1(I) collagen protein sequence, and on hybridization to pro alpha 1(I) mRNA on Northern blots. A comparison of the nucleotide sequence of these clones with the sequence of the 5' end of the pro alpha 2(I) collagen mRNA confirms that there is 84% homology in a 49-bp region surrounding the translation start point, and shows that there is 70% homology in the nucleotide sequences encoding the N-propeptide triple helical region of the two type-I collagen chains.

Elastin mRNA levels during foetal development of sheep nuchal ligament and lung. Hybridization to complementary and cloned DNA

Elastin mRNA levels were quantified in sheep nuchal ligament and lung during the latter half of foetal development with elastin-specific cDNA (complementary DNA) probes using both hybridization in solution (saturation analysis) and hybridization on a fixed support (Northern analysis). For the solution-hybridization studies, cDNA prepared from nuchal-ligament mRNA was enriched to 65% for elastin sequences by hybridizing it to its template at a R0t (mol X s X litre-1) value that included only the abundant class of mRNA sequences. Hybridization of this probe to RNA extracted from nuchal ligament between 70 and 138 days after conception demonstrated elastin sequences increased about 10-fold (from 0.047 to 0.438% of total RNA). In contrast, lung elastin mRNA levels increased only 3-fold (from 0.009 to 0.022% of total RNA) during the same period. Over this development period these values correspond to increases in the average number of elastin mRNA molecules from 950 to 20 000 molecules/ligament cell and from 130 to 330 molecules/lung cell. For Northern analysis, elastin mRNA was purified from near-term-sheep nuchal ligament on sucrose density gradients. Analysis of the translation products of this elastin mRNA showed that relative elastin precursor synthesis was at least 80% of total [3H]valine incorporation. The Mr of this elastin mRNA, determined by methylmercury-agarose-gel electrophoresis, was approx. 1.25 X 10(6). Northern hybridization of nuchal ligament and lung RNA to a [32P]cDNA probe, transcribed from this sucrose-gradient-purified elastin mRNA, confirmed the developmental changes in elastin mRNA levels detected by solution-hybridization techniques. The specificity of this method was confirmed by using a cloned elastin gene fragment. These studies demonstrate that elastin mRNA levels in organs such as nuchal ligament and lung increase with foetal development, but that there are significant differences in the average cellular elastin mRNA content of these two organs.

Control of type I collagen synthesis: evidence for pretranslational coordination of pro alpha 1 (I) and pro alpha 2 (I) chain synthesis in embryonic chick bone

The normal type I collagen molecule contains two alpha 1 (I) chains and one alpha 2 (I) chain. In embryonic chick calvaria, the two-chains are synthesized in a 2:1 ratio, and total polysomes from this tissue contain twice as much mRNA for pro alpha 1 (I) as for pro alpha 2 (I). To further investigate the mechanism by which synthesis may be coordinated, RNA isolated from various cell fractions of embryonic chick calvaria was translated in a rabbit reticulocyte lysate cell-free system. The procollagen chain products were separated by gel-electrophoresis and densitometrically quantitated from autoradiograms of the gels. Total cellular RNA, total cytoplasmic RNA, and polysomal RNA each directed the synthesis of pro alpha 1 (I) and pro alpha 2 (I) in a proportion of 2:1, whereas no procollagen mRNA activity was found in nonpolysomal cytoplasmic RNA. These results indicate that in the chick bone cells, all compartments contain twice as much pro alpha 1 (I) mRNA as pro alpha (I) mRNA, and that virtually all procollagen mRNA in the cytoplasm in polysome-bound. The coordination of procollagen chain synthesis thus presumably occurs at a pretranslational level, through differential rates of formation and/or degradation of the two mRNAs.

Type I osteogenesis imperfecta: a nonfunctional allele for pro alpha 1 (I) chains of type I procollagen

Type I osteogenesis imperfecta (OI) is a dominantly inherited disease characterized clinically by bone fractures during childhood, blue sclerae, and frequent hearing loss accompanied by a decreased content of type I collagen in bone and skin. Cultured skin fibroblasts from three individuals affected with the disease produce half-normal levels of type I procollagen, a disulfide-bonded trimer that contains two pro alpha 1(I) chains and one pro alpha 2(I) chain. In normal cells, pro alpha 1(I) and pro alpha 2(I) are synthesized in a 2:1 ratio and only assembled molecules are secreted. In contrast, the OI cells contain equimolar amounts of pro alpha 1(I) and pro alpha 2(I), which suggests that trimer assembly and secretion are limited by the level of pro alpha 1(I) synthesis. The "extra" pro alpha 2(I) in the OI cells is in a nondisulfide-bonded configuration and is not secreted but apparently contributes to an increased level of intracellular degradation. Thus, decreased production of type I procollagen in these patients is the result of decreased synthesis of pro alpha 1(I). These results suggest that the stoichiometry of pro alpha chains in type I procollagen is determined by the conformation of the chains rather than the ratio in which they are synthesized, that molecules containing more than a single pro alpha 2(I) chain are not assembled, and that the production of this heteropolymeric molecule may be effectively regulated by controlling the synthesis of only one of the subunits.

Cell-free synthesis of putative type V procollagen chains programmed by Chinese hamster lung cell mRNA

A messenger RNA fraction isolated from cultured Chinese hamster lung (CHL) cells programs in a cell-free system prepared from wheat germ the efficient incorporation of [14C] proline into newly synthesized protein with a significant fraction of the incorporated substrate being digestible with bacterial collagenase. This reaction requires both subcellular fractions, an energy source, and is inhibited by the antibiotic puromycin. The relative amount of collagenase-digestible to non-digestible cell-free product depends upon the ratio of CHL mRNA to wheat germ lysate, is not affected by either the Mg2+ or K+ concentrations employed, and under optimal condition, approximately 38% of the total incorporated substrate is collagenase-sensitive. Electrophoresis on SDS-polyacrylamide gels of the products programmed by CHL mRNA indicates that the collagenase-digestible material corresponds in size to a procollagen chain with an apparent molecular mass of approximately 170,000 daltons. These studies suggest that the collagen alpha 1 (V) chain is initially synthesized as a precursor procollagen chain and demonstrate that a significant amount of the mRNA in Chinese hamster lung cells codes for this protein.

R-loop hybridization of collagen DNA: separation in Cs2SO4 gradients

High molecular weight poly(A)RNA (26-35 S) from chicken embryo trunks which is enriched for collagen mRNA was iodinated and hybridized to DNA under conditions of R-loop formation. The R-loops were separated in Cs2SO4 gradients from the bulk of DNA yielding double stranded DNA enriched for collagen genes.