Recombinant protein SMB(PRG4) containing two Somatomedin B domains and a small amount of glycosylation of repetitive sequences of proteoglycan 4 was cloned according to PGR4 gene polymorphism. Mature purification process was established and recombinant protein SMB(PRG4), with high-level expression was purified. By using size-exclusion chromatogaraphy and dynamic light scattering, we found that the recombinant protein self-aggregate to dimeric form. Structure prediction and non-reducing electrophoresis revealed that SMB(PRG4), was a non-covalently bonded dimer.
Glycosylation ; Protein Multimerization ; Proteoglycans ; chemistry ; Recombinant Proteins ; chemistry ; Somatomedins ; chemistry

'Divide and conquer' has been the guiding strategy for the study of protein structure and function. Proteins are divided into domains with each domain having a canonical structural definition depending on its type. In this review, we push forward with the interesting observation that many domains have regions outside of their canonical definition that affect their structure and function; we call these regions 'extensions'. We focus on the highly abundant PDZ (PSD-95, DLG1 and ZO-1) domain. Using bioinformatics, we find that many PDZ domains have potential extensions and we developed an openly-accessible website to display our results ( http://bcz102.ust.hk/pdzex/ ). We propose, using well-studied PDZ domains as illustrative examples, that the roles of PDZ extensions can be classified into at least four categories: 1) protein dynamics-based modulation of target binding affinity, 2) provision of binding sites for macro-molecular assembly, 3) structural integration of multi-domain modules, and 4) expansion of the target ligand-binding pocket. Our review highlights the potential structural and functional importance of domain extensions, highlighting the significance of looking beyond the canonical boundaries of protein domains in general.
Animals ; Binding Sites ; Humans ; Ligands ; PDZ Domains ; Protein Binding ; Protein Multimerization ; Proteins ; chemistry

The c-Abl nonreceptor tyrosine kinase is activated in the cellular responses to genotoxic, oxidative and other forms of stress. Using tagged forms of c-Abl, the present studies demonstrate that c-Abl forms homodimers in cells. The results show that the c-Abl N-terminal regions interact with the corresponding C-terminal regions of both partners in the dimmer. Specifically, the c-Abl SH3 domain binds to a proline-rich motif at amino acids 958-982 in the c-Abl C-terminal region. Deletion of the proline-rich motif disrupts dimmer formation. These findings provide the first evidence that c-Abl forms homodimers and indicate that homodimerization can contribute to the regulation of c-Abl activity.
Humans ; Protein Multimerization ; Proto-Oncogene Proteins c-abl ; genetics ; metabolism ; src Homology Domains

OBJECTIVETo observe changes in plasma thrombomodulin (TM) and D-dimer (DD) levels in neonates with sepsis, and to investigate their significance in evaluating the patients' condition and prognosis.

METHODSFifty-six neonates with sepsis were classified into extremely critical (n=13), critical (n=22) and non-critical groups (n=21) based on neonatal critical illness score (NCIS). Fasting venous blood samples were collected on admission and in the recovery phase. Plasma TM and D-dimer levels were measured using enzyme-linked immunosorbent assay and immune turbidimetry, respectively. Twenty-six healthy neonates were selected as the control group. Plasma TM and D-dimer levels were compared between groups, and the changes after treatment were determined.

RESULTSPlasma TM levels in the extremely critical, critical and non-critical groups were 25.5±6.6, 17.3±4.7 and 13.3±2.8 µg/L respectively, significantly higher than in the control group (9.8±2.7 µg/L) (P<0.01). Plasma D-dimer levels in the extremely critical and critical groups were 744±262 and 436±147 µg/L respectively, also significantly higher than in the control group (205±61 µg/L) (P<0.01). The extremely critical group had significantly higher plasma TM and DD levels than the critical group (P<0.05), and the critical group had significantly higher plasma TM and DD levels than the non-critical group (P<0.05). All patients showed significant decreases in plasma TM and DD levels in the recovery phase after treatment (P<0.01). Plasma TM and DD levels were significantly negatively correlated with NCIS (r=-0.428, P<0.01; r=-0.363, P<0.01).

CONCLUSIONSDetermination of plasma TM and DD levels may be helpful in evaluating severity and prognosis in neonates with sepsis.

Female ; Fibrin Fibrinogen Degradation Products ; analysis ; Humans ; Infant, Newborn ; Male ; Protein Multimerization ; Sepsis ; blood ; Thrombomodulin ; blood

Nascent polypeptide associated complex (NAC) and its two isolated subunits, αNAC and βNAC, play important roles in nascent peptide targeting. We determined a 1.9 Å resolution crystal structure of the interaction core of NAC heterodimer and a 2.4 Å resolution crystal structure of αNAC NAC domain homodimer. These structures provide detailed information of NAC heterodimerization and αNAC homodimerization. We found that the NAC domains of αNAC and βNAC share very similar folding despite of their relative low identity of amino acid sequences. Furthermore, different electric charge distributions of the two subunits at the NAC interface provide an explanation to the observation that the heterodimer of NAC complex is more stable than the single subunit homodimer. In addition, we successfully built a βNAC NAC domain homodimer model based on homologous modeling, suggesting that NAC domain dimerization is a general property of the NAC family. These 3D structures allow further studies on structure-function relationship of NAC.
Amino Acid Sequence ; Dimerization ; Humans ; Molecular Chaperones ; chemistry ; Peptides ; metabolism ; Protein Multimerization

Bone morphogenetic protein (BMP) homodimers are of significant osteoinductivity. However, their clinical application is limited because of high effective dosage. Recently, BMP heterodimers are reported to address the issue. This is a review of the researches on BMP heterodimers, including existent evidences, types and synthetic methods, biological activities in comparison to BMP homodimers and possible mechanisms, further research direction and future expectations.
Animals ; Biopolymers ; Bone Morphogenetic Protein 2 ; Bone Morphogenetic Protein 7 ; Bone Morphogenetic Proteins ; genetics ; pharmacology ; Humans ; Protein Multimerization

In order to explore the potential influences of the disulfide bridge on the physical and chemical properties of PrP protein, the expressed recombinant human wild-type PrP protein was purified for using in an established redox process for the reduction and oxidation of the ethanethiol group within PrP. Sedimentation tests illustrated that redox process remarkably promoted the aggregation of recombinant PrP. Thioflavin T binding assay revealed an enhanced fibrillization of the recombinant human PrP after redox process. Far-UV circular dichroism demonstrated that the PrP treated with redox process showed a significant p-sheet rich structure. Furthermore, PrP-specific Western blot identified that the recombinant PrP after redox possessed stronger proteinase K-resistance. Those data indicates that the formation of the disulfide bridge induces the alteration of the secondary structure and enhances the progresses of aggregation and fibrillization of PrP protein.
Amyloid ; chemistry ; Endopeptidase K ; metabolism ; Humans ; Oxidation-Reduction ; Prions ; chemistry ; metabolism ; Protein Multimerization ; Protein Structure, Secondary ; Proteolysis ; Sulfhydryl Compounds ; chemistry

The cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel that belongs to the ATP-binding cassette (ABC) transporter superfamily. Defective function of CFTR is responsible for cystic fibrosis (CF), the most common lethal autosomal recessive disorder in Caucasian populations. The disease is manifested in defective chloride transport across the epithelial cells in various tissues. To date, more than 1400 different mutations have been identified as CF-associated. CFTR is regulated by phosphorylation in its regulatory (R) domain, and gated by ATP binding and hydrolysis at its two nucleotide-binding domains (NBD1 and NBD2). Recent studies reveal that the NBDs of CFTR may dimerize as observed in other ABC proteins. Upon dimerization of CFTR's two NBDs, in a head-to-tail configuration, the two ATP-binding pockets (ABP1 and ABP2) are formed by the canonical Walker A and B motifs from one NBD and the signature sequence from the partner NBD. Mutations of the amino acids that interact with ATP reveal that the two ABPs play distinct roles in controlling ATP-dependent gating of CFTR. It was proposed that binding of ATP to the ABP2, which is formed by the Walker A and B in NBD2 and the signature sequence in NBD1, is critical for catalyzing channel opening. While binding of ATP to the ABP1 alone may not increase the opening rate, it does contribute to the stabilization of the open channel conformation. Several disease-associated mutations of the CFTR channel are characterized by gating defects. Understanding how CFTR's two NBDs work together to gate the channel could provide considerable mechanistic information for future pharmacological studies, which could pave the way for tailored drug design for therapeutical interventions in CF.
Adenosine Triphosphate ; physiology ; Animals ; Binding Sites ; Cystic Fibrosis Transmembrane Conductance Regulator ; physiology ; Humans ; Hydrolysis ; Protein Interaction Domains and Motifs ; Protein Multimerization

Hepatitis E is a main cause of acute viral hepatitis in developing countries where it occurs as sporadic cases and in epidemics form. The causative agent, hepatitis E virus, is transmitted primarily by the fecal-oral route. The approximately 7.5 kb positive-sense single-strand RNA genome includes three open reading frames (ORFs), one of which (ORF2) is postulated to encode the major viral capsid protein (pORF2) of 660 amino acid residues. We earlier showed that a bacterially expressed peptide, designated as NE2, located from amino acid residues 394 to 606 of ORF2, was found to aggregate into homodimer to at least hexamer. To understand the interface domains within this peptide vital for dimerization and formation of major neutralizing epitopes, NE2 protein underwent terminal-truncated and site-directed mutation. The hydrophobic region, ORF2 aa597-aa602 (AVAVLA), played a key role in oligomerization. Any amino acid residue of this region replaced with glutamic acid residue, the peptide can not refold as homodimer and/or oligomer. The immunoreactivities of these mutant peptides, blotted with anti-HEV neutralizing monoclonal antibody (8C11) and convalescent human sera, show associated to the formation of homodimer. The intermolecular contact region on homodimer was investigated by chemical cross-linking of two site-directed cysteines. When the alanine on aa597 site mutated with cysteine, two different homodimers were found in SDS-PAGE analysis. One (42kD) can be disassociated with 8mol/L urea, which is postulated to form by virtue of hydrophobic interaction, and the other (60kD) falls apart with the reductant DTT present. The exact conformation, generating the cross-linking reaction of cysteines, was further investigated by induced-oxidation on monomer and hydrophobic homodimer of A597C protein with GSH/GSSG. And the results revealed, it is the conformation of hydrophobic homodimer that induces the disulfide bond come into being, instead of the one of monomer. So the aa597 site was verified to be located on interface domain of hydrophobically interacting homodimeric complex. To evaluate the biological significance of hydrophobicity of interface domain, we searched natural variations as to the region on all available databases with NCBI blast program. All variations on these amino acid residues kept higher hydrophobicity, which suggests that the hydrophobic domain is critical for the assemblage and propagation of HEV. NE2 N-terminal deletions up to aa458 had no effect on dimerization and took no exact part in formation of major neutralizing epitopes, but the fragment may act as helper for the formation of major neutralizing epitopes on NE2. Interestingly, the C-terminus aa605-aa660 of ORF2 can also act as helper instead of the N-terminus of NE2. This study suggests an interface domain of NE2 might be vital for HEV capsomer assembly and formation of major neutralizing epitopes. These results may offer clues to the rational design of recombinant anti-HEV vaccine.
Capsid Proteins ; chemistry ; Hepatitis E virus ; chemistry ; Hydrophobic and Hydrophilic Interactions ; Protein Multimerization ; Protein Structure, Tertiary ; Virus Assembly

Cell Cycle Proteins ; chemistry ; Histones ; chemistry ; Humans ; Minichromosome Maintenance Complex Component 2 ; chemistry ; Models, Molecular ; Protein Multimerization ; Protein Structure, Quaternary