title: New tricks for "old" domains: how novel architectures and promiscuous hubs contributed to the organization and evolution of the ECM.
abstract: The extracellular matrix (ECM) is a defining characteristic of metazoans and consists of a meshwork of self-assembling, fibrous proteins, and their functionally related neighbours. Previous studies, focusing on a limited number of gene families, suggest that vertebrate complexity predominantly arose through the duplication and subsequent modification of retained, preexisting ECM genes. These genes provided the structural underpinnings to support a variety of specialized tissues, as well as a platform for the organization of spatio-temporal signaling and cell migration. However, the relative contributions of ancient versus novel domains to ECM evolution have not been quantified across the full range of ECM proteins. Here, utilizing a high quality list comprising 324 ECM genes, we reveal general and clade-specific domain combinations, identifying domains of eukaryotic and metazoan origin recruited into new roles in approximately two-third of the ECM proteins in humans representing novel vertebrate proteins. We show that, rather than acquiring new domains, sampling of new domain combinations has been key to the innovation of paralogous ECM genes during vertebrate evolution. Applying a novel framework for identifying potentially important, noncontiguous, conserved arrangements of domains, we find that the distinct biological characteristics of the ECM have arisen through unique evolutionary processes. These include the preferential recruitment of novel domains to existing architectures and the utilization of high promiscuity domains in organizing the ECM network around a connected array of structural hubs. Our focus on ECM proteins reveals that distinct types of proteins and/or the biological systems in which they operate have influenced the types of evolutionary forces that drive protein innovation. This emphasizes the need for rigorously defined systems to address questions of evolution that focus on specific systems of interacting proteins.
authors.affiliation: Program in Molecular Structure and Function, Hospital for Sick Children, Toronto, Ontario, Canada Department of Molecular Genetics, University of Toronto, Ontario, Canada.
authors.forename: Graham
authors.initials: G
authors.lastname: Cromar
authors.affiliation: Department of Computer Science, University of Toronto, Ontario, Canada Terrence Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Ontario, Canada.
authors.forename: Ka-Chun
authors.initials: KC
authors.lastname: Wong
authors.affiliation: Program in Molecular Structure and Function, Hospital for Sick Children, Toronto, Ontario, Canada.
authors.forename: Noeleen
authors.initials: N
authors.lastname: Loughran
authors.affiliation: Program in Molecular Structure and Function, Hospital for Sick Children, Toronto, Ontario, Canada Department of Molecular Genetics, University of Toronto, Ontario, Canada.
authors.forename: Tuan
authors.initials: T
authors.lastname: On
authors.affiliation: Program in Molecular Structure and Function, Hospital for Sick Children, Toronto, Ontario, Canada.
authors.forename: Hongyan
authors.initials: H
authors.lastname: Song
authors.affiliation: Program in Molecular Structure and Function, Hospital for Sick Children, Toronto, Ontario, Canada.
authors.forename: Xuejian
authors.initials: X
authors.lastname: Xiong
authors.affiliation: Department of Molecular Genetics, University of Toronto, Ontario, Canada Department of Computer Science, University of Toronto, Ontario, Canada Terrence Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Ontario, Canada Banting and Best Department of Medical Research, University of Toronto, Ontario, Canada.
authors.forename: Zhaolei
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Program in Molecular Structure and Function, Hospital for Sick Children, Toronto, Ontario, Canada Department of Molecular Genetics, University of Toronto, Ontario, Canada Department of Biochemistry, University of Toronto, Ontario, Canada john.parkinson@utoronto.ca.
authors.forename: John
authors.initials: J
authors.lastname: Parkinson
mesh_terms: D000818:Animals; D019143:Evolution, Molecular; D005109:Extracellular Matrix / Q000378:metabolism*; D016326:Extracellular Matrix Proteins / Q000378:metabolism*; D006801:Humans; D020080:Tandem Repeat Sequences / Q000235:genetics
chemical_list: D016326:Extracellular Matrix Proteins
keywords: domain architecture; domain networks; evolution; extracellular matrix; protein domains