Latent transforming growth factor beta-binding proteins and fibulins compete for fibrillin-1 and exhibit exquisite specificities in binding sites.
Latent transforming growth factor (TGF) beta-binding proteins (LTBPs) interact with fibrillin-1. This interaction is important for proper sequestration and extracellular control of TGFbeta. Surface plasmon resonance interaction studies show that residues within the first hybrid domain (Hyb1) of fibrillin-1 contribute to interactions with LTBP-1 and LTBP-4. Modulation of binding affinities by fibrillin-1 polypeptides in which residues in the third epidermal growth factor-like domain (EGF3) are mutated demonstrates that the binding sites for LTBP-1 and LTBP-4 are different and suggests that EGF3 may also contribute residues to the binding site for LTBP-4. In addition, fibulin-2, fibulin-4, and fibulin-5 bind to residues contained within EGF3/Hyb1, but mutated polypeptides again indicate differences in their binding sites in fibrillin-1. Results demonstrate that these protein-protein interactions exhibit "exquisite specificities," a phrase commonly used to describe monoclonal antibody interactions. Despite these differences, interactions between LTBP-1 and fibrillin-1 compete for interactions between fibrillin-1 and these fibulins. All of these proteins have been immunolocalized to microfibrils. However, in fibrillin-1 (Fbn1) null fibroblast cultures, LTBP-1 and LTBP-4 are not incorporated into microfibrils. In contrast, in fibulin-2 (Fbln2) null or fibulin-4 (Fbln4) null cultures, fibrillin-1, LTBP-1, and LTBP-4 are incorporated into microfibrils. These data show for the first time that fibrillin-1, but not fibulin-2 or fibulin-4, is required for appropriate matrix assembly of LTBPs. These studies also suggest that the fibulins may affect matrix sequestration of LTBPs, because in vitro interactions between these proteins are competitive.
Ono
Robert N
RN
From the Shriners Hospital for Children, Portland, Oregon 97239.
Sengle
Gerhard
G
Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239.
Charbonneau
Noe L
NL
From the Shriners Hospital for Children, Portland, Oregon 97239.
Carlberg
Valerie
V
Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239.
Bächinger
Hans Peter
HP
From the Shriners Hospital for Children, Portland, Oregon 97239; Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239.
Sasaki
Takako
T
Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239.
Lee-Arteaga
Sui
S
Department of Pharmacology and Systems Therapeutics, Mt. Sinai School of Medicine, New York, New York 10029.
Zilberberg
Lior
L
Department of Cell Biology, New York University Langone Medical Center, New York, New York 10016.
Rifkin
Daniel B
DB
Department of Cell Biology, New York University Langone Medical Center, New York, New York 10016.
Ramirez
Francesco
F
Department of Pharmacology and Systems Therapeutics, Mt. Sinai School of Medicine, New York, New York 10029.
Chu
Mon-Li
ML
Department of Dermatology and Cutaneous Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
Sakai
Lynn Y
LY
From the Shriners Hospital for Children, Portland, Oregon 97239; Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239. Electronic address: lys@shcc.org.
D000818:Animals; D001665:Binding Sites / Q000235:genetics; D001667:Binding, Competitive; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D016326:Extracellular Matrix Proteins / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D000071838:Fibrillin-1; D000071837:Fibrillins; D006801:Humans; D053779:Latent TGF-beta Binding Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D020894:Microfibrils / Q000378:metabolism; D008840:Microfilament Proteins / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D020349:Surface Plasmon Resonance; D054392:Adipokines
D002135:Calcium-Binding Proteins; D016326:Extracellular Matrix Proteins; D000071838:Fibrillin-1; D000071837:Fibrillins; D053779:Latent TGF-beta Binding Proteins; D008840:Microfilament Proteins; D011994:Recombinant Proteins; C403672:EFEMP2 protein, human; C000605722:FBN1 protein, human; D054392:Adipokines; C000605724:Fbn1 protein, mouse; C538753:LTBP-4 protein, mouse; C509033:Ltbp1 protein, mouse; C084612:fibulin 2