title: Streptococcal Scl1 and Scl2 proteins form collagen-like triple helices.
abstract: The collagens are a family of animal proteins containing segments of repeated Gly-Xaa-Yaa (GXY) motifs that form a characteristic triple-helical structure. Genes encoding proteins with repeated GXY motifs have also been reported in bacteria and phages; however, it is unclear whether these prokaryotic proteins can form a collagen-like triple-helical structure. Here we used two recently identified streptococcal proteins, Scl1 and Scl2, containing extended GXY sequence repeats as model proteins. First we observed that prior to heat denaturation recombinant Scl proteins migrated as homotrimers in gel electrophoresis with and without SDS. We next showed that the collagen-like domain of Scl is resistant to proteolysis by trypsin. We further showed that circular dichroism spectra of the Scl proteins contained features characteristic of collagen triple helices, including a positive maximum of ellipticity at 220 nm. Furthermore the triple helices of Scl1 and Scl2 showed a temperature-dependent unfolding with melting temperatures of 36.4 and 37.6 degrees C, respectively, which resembles those seen for collagens. We finally demonstrated by electron microscopy that the Scl proteins are organized into "lollipop-like" structures, similar to those seen in human proteins with collagenous domains. This implies that the repeated GXY tripeptide motif is a structural indicator of collagen-like triple helices in proteins from such phylogenetically distant sources as bacteria and humans.
authors.affiliation: Center for Extracellular Matrix Biology, Institute of Biosciences and Technology, Texas A&M University System Health Science Center, Houston, TX 77030, USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Xu
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Keene
authors.forename: Janusz M
authors.initials: JM
authors.lastname: Bujnicki
authors.forename: Magnus
authors.initials: M
authors.lastname: Höök
authors.forename: Slawomir
authors.initials: S
authors.lastname: Lukomski
mesh_terms: D000483:Alleles; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D015153:Blotting, Western; D002942:Circular Dichroism; D003094:Collagen / Q000737:chemistry / Q000378:metabolism*; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D011485:Protein Binding; D011489:Protein Denaturation; D011994:Recombinant Proteins / Q000378:metabolism; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology; D013291:Streptococcus / Q000378:metabolism*; D013501:Surface-Active Agents / Q000494:pharmacology; D013696:Temperature; D013997:Time Factors
chemical_list: D001426:Bacterial Proteins; D011994:Recombinant Proteins; C423454:Scl1 protein, Streptococcus; C423453:Scl2 protein, Streptococcus; D013501:Surface-Active Agents; D012967:Sodium Dodecyl Sulfate; D003094:Collagen