Tài liệu Báo cáo Y học: BIGH3 (TGFBI) Arg124 mutations influence the amyloid conversion of related

BIGH3 (TGFBI) Arg124 mutations influence the amyloid conversion

of related peptides in vitro

Implications in the BIGH3-linked corneal dystrophies

Clair-Florent Schmitt-Bernard1,2, Alain Chavanieu3

, Gudrun Herrada3

, Guy Subra3

, Bernard Arnaud4

,

Jacques G. Demaille1

, Bernard Calas3 and A´ ngel Argile´ s

1

1

Institut de Ge´ne´tique Humaine, CNRS UPR 1142, Montpellier, France; 2

Antigone Ophtalmologie, Montpellier, France; 3

Centre de

Biochimie Structurale, CNRS UMR 5048, Universite´ Montpellier, Montpellier, France; 4

Service d’Ophtalmologie, CMC Gui de

Chauliac, Montpellier, France

Amyloid deposits with Arg124 mutated TGFBI protein

have been identified in autosomal dominant blinding corneal

dystrophies.We assessed in vitro the mechanisms determin￾ing TGFBI protein amyloid transformation involving

mutations of Arg124.Eight peptides synthesized following

the TGFBI protein sequence, centered on codon Arg124

holding the previously reported amyloidogenic mutations

and the respective controls were studied.Cys124 and His124

mutated peptide preparations contained significantly higher

amounts of amyloid than the native peptide.Blocking the

SH group of Cys124 and deleting the first four NH2-terminal

amino acids including Val112-Val113 resulted in a decrease

in amyloid fibril formation while deletion of the nine

CONH2-terminal residues increased amyloid fibril concen￾tration.Fourrier transformed-infrared spectroscopy analysis

of the different peptide solutions showed an increase in

b-pleated sheet structures in those with enhanced amyloid

yielding.We designed a peptide (BB1) likely to counteract

the role of Val112-Val113 in amyloid fibril formation.

Incubation of Cys124 peptide with BB1 indeed resulted in a

35% inhibition of amyloid fibril formation.

Our results are in keeping with the clinical observations of

Arg124 mutation-linked amyloidosis and show the import￾ance of Val112–Val113, disulfide and hydrogen bonding in

increasing the b-pleated conformation and amyloid forma￾tion.These findings shed new light on the molecular mech￾anisms of TGFBI protein amyloidogenesis and encourage

further research on the use of specifically designed peptides

as putative therapeutic agents for these disabling diseases.

Keywords: amyloidosis; keratoepithelin; lattice corneal dys￾trophy; granular corneal dystrophy; synthetic peptide.

Hereditary corneal dystrophies are a cause of blindness.

These dystrophies are characterized by a progressive

alteration of the particular structure of the cornea resulting

in loss of its transparency.Based upon their clinical

characteristics, hereditary corneal dystrophies form a

distinctive group of corneal diseases.Some of them involve

the corneal stroma where deposits begin to appear

during the first decades of life and severely impair visual

acuity in adulthood.Their therapy is restricted to keratopl￾asty and phototherapeutic keratectomy by Excimer laser.

Unfortunately, the benefits of these therapies remain

transient as recurrence of the deposits is the rule.

Genetic studies have recently confirmed that a group of

hereditary corneal dystrophies have a common molecular

mechanism: the involvement of the BIGH3 (TGFBI,

transforming growth factor b-induced) gene [1].Specific

BIGH3 mutations have been linked to particular forms of

the disease in this group of dystrophies.Autosomal

dominant BIGH3-linked corneal dystrophies may present

amyloid deposits, granular deposits or a mixture of both

(granular and amyloid).

The BIGH3 gene encodes for a 683 amino-acid protein

inducible by TGFb, the TGFBI protein also known as

big-h3.It is a prominent constituent of the cornea, skin, and

matrix of many connective tissues [2].It is a secreted protein

with an amino-terminal secretory sequence, a carboxy￾terminal Arg-Gly-Asp sequence and four homologous

domains of 140 amino acids [2].The TGFBI protein, as

other homologous proteins, may interfere in the cell

adhesion process.The Arg-Gly-Asp sequence is known to

act as a ligand recognition site for integrins.The particular

integrins with binding capacities for the corneal TGFBI

protein remain to be fully identified.Kim et al.[3] have

recently shown that alpha3-beta1 integrins bind to TGFBI.

Two major sites for mutation have been recognized in the

BIGH3 gene as inducing four distinct hereditary corneal

dystrophies.These mutation sites are located at codon

Arg124 and codon Arg555 [4].Other mutations in the

BIGH3 gene have been occasionally reported [5–11].

Mutations in Arg555 are responsible for corneal dystrophy

of Bowman’s layer type 2 (CDB2, Thiel-Behnke corneal

Correspondence to C.-F. Schmitt-Bernard, IGH CNRS UPR 1142,

141, rue de la Cardonille, F-34396 Montpellier cedex 5, France.

Fax: + 33 4 67 42 39 73, Tel.: + 33 4 67 42 09 83,

E-mail: [email protected]

Abbreviations: BIGH3, beta-induced gene-human 3; big-h3, BIGH3

gene product; TGFBI, transforming growth factor beta-induced gene;

TGFb, transforming growth factor beta; LCD, lattice corneal dys￾trophy; CDB, corneal dystrophy of Bowman’s layer; GCD, granular

corneal dystrophy; ThT, thioflavin T.

(Received 5 March 2002, revised 6 August 2002,

accepted 23 August 2002)

Eur. J. Biochem. 269, 5149–5156 (2002)
FEBS 2002 doi:10.1046/j.1432-1033.2002.03205.x