The evolution of proteins is primarily driven by the combinatorial assembly of a limited set of pre-existing modules known as protein domains. This modular architecture not only supports the diversity of natural proteins but also provides a robust strategy for protein engineering, enabling the design of artificial proteins with enhanced or novel functions for various industrial applications. Among these functions, oligomerization plays a crucial role in enhancing protein activity, such as by increasing the binding capacity of antibodies. To investigate the potential of engineering oligomerization, we examined the transferability of the sequence domain encoded by exon 5 (Ex5), which was originally responsible for the oligomerization of ameloblastin (AMBN). We designed a two-domain protein composed of Ex5 in combination with a monomeric, globular, and highly stable protein, specifically calmodulin (CaM). CaM represents the opposite protein character to AMBN, which is highly disordered and has a dynamic character. This engineered protein, termed eCaM, successfully acquired an oligomeric function, inducing self-assembly under specific conditions. Biochemical and biophysical analyses revealed that the oligomerization of eCaM is both concentration- and time-dependent, with the process being reversible upon dilution. Furthermore, mutating a key oligomerization residue within Ex5 abolished the self-assembly of eCaM, confirming the essential role of the Ex5 motif in driving oligomerization. Our findings demonstrate that the oligomerization properties encoded by Ex5 can be effectively transferred to a new protein context, though the positioning of Ex5 within the protein structure is critical. This work highlights the potential of enhancing monomeric proteins with oligomeric functions, paving the way for industrial applications and the development of proteins with tailored properties.

• Publication type
• Journal Article MeSH

Ameloblastin is a protein in biomineralization of tooth enamel. However recent results indicate that this is probably not its only role in an organism. Enamel matrix formation represents a complex process enabled via specific crosslinking of two proteins - the most abundant amelogenin and the ameloblastin (AMBN). The human AMBN (hAMBN) gene possesses 13 protein coding exons with alternatively spliced transcripts and the longest isoform about 447 amino acid residues. It has been described that AMBN molecules in vitro assemble into oligomers via a sequence encoded by exon 5. Enamel is formed by the processing of enamel proteins by two specific proteases - enamelysin (MMP-20) and kallikrein 4 (KLK-4). The scaffold made of AMEL and non-amelogenin proteins is cleaved and removed from the developed tooth enamel. The hAMBN is expressed in two isoforms (ISO I and II), which could lead to their different utilization determined by distinct proteolytic profiles. In this study, we compared proteolytic profiles of both isoforms of hAMBN expressed in E. coli after proteolysis by MMP-20, KLK-4, and their 1:2 mixture. Proteolysis products were analysed and cleavage sites were identified by mass spectrometry. The proteolytic profiles of two AMBN isoforms showed different results, although we have to determine that the analysed AMBN was not post-translationally modified as expressed in prokaryotic cells. These results may lead to the suggestion of potentially divergent roles of AMBN isoforms cleavage products in various cell signalling pathways such as calcium buffering or signalling cascades.

• Keywords
• Ameloblastin, Enzymatic cleavage products, KLK-4, MMP-20, Proteolytic analysis,
• Publication type
• Journal Article MeSH

Highly specialized enamel matrix proteins (EMPs) are predominantly expressed in odontogenic tissues and diverged from common ancestral gene. They are crucial for the maturation of enamel and its extreme complexity in multiple independent lineages. However, divergence of EMPs occured already before the true enamel evolved and their conservancy in toothless species suggests that non-canonical functions are still under natural selection. To elucidate this hypothesis, we carried out an unbiased, comprehensive phenotyping and employed data from the International Mouse Phenotyping Consortium to show functional pleiotropy of amelogenin, ameloblastin, amelotin, and enamelin, genes, i.e. in sensory function, skeletal morphology, cardiovascular function, metabolism, immune system screen, behavior, reproduction, and respiratory function. Mice in all KO mutant lines, i.e. amelogenin KO, ameloblastin KO, amelotin KO, and enamelin KO, as well as mice from the lineage with monomeric form of ameloblastin were affected in multiple physiological systems. Evolutionary conserved motifs and functional pleiotropy support the hypothesis of role of EMPs as general physiological regulators. These findings illustrate how their non-canonical function can still effect the fitness of modern species by an example of influence of amelogenin and ameloblastin on the bone physiology.

• MeSH
• Amelogenin metabolism   MeSH
• Mice MeSH
• Dental Enamel Proteins * genetics   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Amelogenin MeSH
• enamel matrix proteins MeSH Browser
• Dental Enamel Proteins * MeSH

Bone defect is a noteworthy health problem and is the second most transplanted tissue after blood. Numerous bone grafts are designed and applied in clinics. Limitations, however, from different aspects still exist, including limited supply, mechanical strength, and bioactivity. In this study, two biomimetic peptides (P2 and P6) are incorporated into a composite bioactive xeno hybrid bone graft named SmartBonePep®, with the aim to increase the bioactivity of the bone graft. The results, which include cytotoxicity, proliferation rate, confocal microscopy, gene expression, and protein qualification, successfully prove that the SmartBonePep® has multi-modal biological effects on human mesenchymal stem cells from bone marrow. The effective physical entrapment of P6 into a composite xeno-hybrid bone graft, withstanding manufacturing processes including exposure to strong organic solvents and ethylene oxide sterilization, increases the osteogenic potential of the stem cells as well as cell attachment and proliferation. P2 and P6 both show a strong biological potential and may be future candidates for enhancing the clinical performance of bone grafts.

• Keywords
• bioactive proteins, bone graft, bone regeneration biomimetic, bone scaffold, intrinsically disordered, mesenchymal stem cells, xenograft,
• Publication type
• Journal Article MeSH

Ameloblastin (Ambn) as an intrinsically disordered protein (IDP) stands for an important role in the formation of enamel-the hardest biomineralized tissue commonly formed in vertebrates. The human ameloblastin (AMBN) is expressed in two isoforms: full-length isoform I (AMBN ISO I) and isoform II (AMBN ISO II), which is about 15 amino acid residues shorter than AMBN ISO I. The significant feature of AMBN-its oligomerization ability-is enabled due to a specific sequence encoded by exon 5 present at the N-terminal part in both known isoforms. In this study, we characterized AMBN ISO I and AMBN ISO II by biochemical and biophysical methods to determine their common features and differences. We confirmed that both AMBN ISO I and AMBN ISO II form oligomers in in vitro conditions. Due to an important role of AMBN in biomineralization, we further addressed the calcium (Ca2+)-binding properties of AMBN ISO I and ISO II. The binding properties of AMBN to Ca2+ may explain the role of AMBN in biomineralization and more generally in Ca2+ homeostasis processes.

• Keywords
• ameloblastin, biomineralization, calcium binding, intrinsically disordered protein (IDPs), oligomerization,
• MeSH
• Models, Biological MeSH
• Hydrodynamics MeSH
• Humans MeSH
• Protein Multimerization MeSH
• Protein Isoforms MeSH
• Calcium-Binding Proteins chemistry   metabolism   MeSH
• Dental Enamel Proteins chemistry   metabolism   MeSH
• Spectrum Analysis MeSH
• Temperature MeSH
• Calcium metabolism   MeSH
• Protein Binding MeSH
• Intrinsically Disordered Proteins metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• AMBN protein, human MeSH Browser
• Protein Isoforms MeSH
• Calcium-Binding Proteins MeSH
• Dental Enamel Proteins MeSH
• Calcium MeSH
• Intrinsically Disordered Proteins MeSH

Ameloblastin (AMBN), an important component of the self-assembled enamel extra cellular matrix, contains several in silico predicted phosphorylation sites. However, to what extent these sites actually are phosphorylated and the possible effects of such post-translational modifications are still largely unknown. Here we report on in vitro experiments aimed at investigating what sites in AMBN are phosphorylated by casein kinase 2 (CK2) and protein kinase A (PKA) and the impact such phosphorylation has on self-assembly and calcium binding. All predicted sites in AMBN can be phosphorylated by CK2 and/or PKA. The experiments show that phosphorylation, especially in the exon 5 derived part of the molecule, is inversely correlated with AMBN self-assembly. These results support earlier findings suggesting that AMBN self-assembly is mostly dependent on the exon 5 encoded region of the AMBN gene. Phosphorylation was significantly more efficient when the AMBN molecules were in solution and not present as supramolecular assemblies, suggesting that post-translational modification of AMBN must take place before the enamel matrix molecules self-assemble inside the ameloblast cell. Moreover, phosphorylation of exon 5, and the consequent reduction in self-assembly, seem to reduce the calcium binding capacity of AMBN suggesting that post-translational modification of AMBN also can be involved in control of free Ca2+ during enamel extra cellular matrix biomineralization. Finally, it is speculated that phosphorylation can provide a functional crossroad for AMBN either to be phosphorylated and act as monomeric signal molecule during early odontogenesis and bone formation, or escape phosphorylation to be subsequently secreted as supramolecular assemblies that partake in enamel matrix structure and mineralization.

• Keywords
• Ca2+- binding, ameloblastin, casein kinase 2, enamel, intrinsically disordered proteins, phosphorylation, protein kinase A, self-assembly,
• Publication type
• Journal Article MeSH