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Localization of viral-envelope-glycoprotein-binding sites in fibronectin.

ABSTRACT: Purified viral-envelope glycoproteins from influenza A virus were found to bind to two fragments of the fibronectin molecule. Human plasma fibronectin was digested by leucocyte cathepsin G, and three different fragments, of Mr 30000, 40000 and 12000-140000, with specific binding functions were isolated. Micelles of radiolabelled influenza A glycoprotein were allowed to bind to these fragments immobilized on polystyrene micro-titre wells. The C-terminal 120000-14000-Mr fragments that carry the cell-binding activity bound viral proteins most efficiently, whereas the 40000-Mr gelatin-binding fragment bound considerably less. The N-terminal 30000-Mr Staphylococcus aureus-binding fragment was negative in the assays. Laminin, a basement-membrane protein, also bound viral proteins, though less effectively than fibronectin. The binding was abolished if laminin or fibronectin fragments were pretreated with neuraminidase. This suggests that the sialic acids in the sugar moieties of these glycoproteins are involved in the binding. The affinity of viral-envelope glycoproteins for certain domains of fibronectin and for laminin may play a role in virus-cell interactions.

SUBMITTER: Julkunen I

PROVIDER: S-EPMC1153498 | biostudies-other | 1984 Apr

REPOSITORIES: biostudies-other

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Fibronectin binding to complement subcomponent C1q. Localization of their respective binding sites.

Project description:The interaction of purified human plasma fibronectin with the C1q subcomponent of complement was investigated by using a solid-phase radiobinding assay. 125I-fibronectin binding to native C1q, purified collagen domain (C1q-c) or globular domain (C1q-g) was compared. When the purified domains were insolubilized by binding to plastic, the C1q-c exhibited 59% of the binding demonstrated with intact C1q, whereas the C1q-g exhibited 35% of the binding. N-Terminal sequencing of the globular domain showed that a sequence of seven collagen-like amino acids was retained on each chain of the C1q-g fragment. 125I-fibronectin binding to C1q could be inhibited equally well by fluid-phase C1q and C1q-c, but not by fluid-phase C1q-g, implying that the collagen-like region retained on the C1q-g is masked in the fluid phase. In addition, studies were performed to determine which subunit(s) of C1q bind(s) fibronectin. The percentages of fibronectin bound by the A, B, and C chain of C1q were found to be 38, 21 and 41% respectively. Inhibition studies with purified 200-180 kDa, 50 kDa or 29 kDa fragments of fibronectin show that the binding site on fibronectin for C1q is the 50 kDa gelatin-binding domain.

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Project description: Not available

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