Recombinant Nautilus macromphalus Uncharacterized protein SMPP3

Basic Research Questions

• What is Nautilus macromphalus Uncharacterized protein SMPP3?

  SMPP3 (Shell Matrix Protein P3) is one of several uncharacterized proteins isolated from the shell of Nautilus macromphalus (Bellybutton nautilus), a cephalopod that has retained its external biomineralized shell unlike most modern cephalopods . Shell Matrix Proteins (SMPs) are present in trace amounts within mollusk shells but play essential roles in shell formation and structural maintenance, including calcium carbonate nucleation, crystal growth regulation, and polymorph selection . SMPP3 was identified through multiomics approaches combining transcriptomics of mantle tissue with proteomics of shell matrix extracts . Its exact function remains to be elucidated, but as part of the shell matrix protein complex, it likely contributes to the biomineralization processes that are crucial for shell development in this ancient cephalopod lineage.

• How has SMPP3 been identified and isolated from Nautilus macromphalus?

  SMPP3 was identified through a sophisticated multiomics approach that includes:

  • Transcriptome sequencing of mRNA extracted from mantle tissue samples

  • Assembly of sequencing reads to generate contigs

  • Extraction of total proteins from the shell using specialized protocols

  • Digestion of extracted proteins into peptides using trypsin

  • Analysis of peptides via Liquid Chromatography-Mass Spectrometry/Mass Spectrometry (LC-MS/MS)

  • Comparison of obtained protein spectra with inferred protein spectra from transcriptome contigs

  • Sequence annotation through BLASTp searches against protein databases

  • Domain prediction using multiple bioinformatic tools (SMART, PROSITE, InterProScan, NCBI, Pfam)

  This systematic approach has allowed researchers to identify shell-specific proteins, including SMPP3, from the complex mixture of proteins present in the Nautilus shell.

• What expression systems are available for producing recombinant SMPP3?

  Recombinant SMPP3 can be produced in multiple expression systems, each with distinct advantages:

  Expression System	Catalog Code	Advantages	Considerations
  E. coli	CSB-EP307726NBA	High yield, cost-effective, rapid production	Limited post-translational modifications
  Yeast	CSB-YP307726NBA	Some eukaryotic post-translational modifications	Moderate yield
  Baculovirus	CSB-BP307726NBA	Complex eukaryotic post-translational modifications	Higher cost, longer production time
  Mammalian cell	CSB-MP307726NBA	Most authentic post-translational modifications	Lower yield, highest cost
  E. coli (Biotinylated)	CSB-EP307726NBA-B	Site-specific biotinylation via AviTag-BirA technology	Specialized applications

  The choice of expression system should be determined by research requirements, particularly regarding protein folding, post-translational modifications, and downstream applications .

• What are the optimal storage and handling conditions for recombinant SMPP3?

  For optimal stability and activity of recombinant SMPP3, the following storage and handling conditions are recommended:

  • Store at -20°C for regular storage, or -80°C for extended storage periods

  • Avoid repeated freeze-thaw cycles which can lead to protein degradation

  • Store working aliquots at 4°C for up to one week

  • Briefly centrifuge vials prior to opening to bring contents to the bottom

  • Reconstitute lyophilized protein in deionized sterile water to a concentration of 0.1-1.0 mg/mL

  • Add 5-50% glycerol (final concentration) and aliquot for long-term storage

  • The shelf life is approximately 6 months for liquid form and 12 months for lyophilized form when stored properly

  Following these protocols will help maintain protein integrity and biological activity for research applications.

• What is the amino acid sequence and basic properties of SMPP3?

  While the search results don't provide the complete amino acid sequence specifically for SMPP3, we can examine the properties based on available information:

  • SMPP3 is cataloged under UniProt accession P85388.1

  • The protein has relatively high purity (>85%) when analyzed by SDS-PAGE

  • It belongs to a family of uncharacterized shell matrix proteins from Nautilus macromphalus

  • For context, related proteins from the same organism have known sequences:

    • SMPP1: "SDCACLHALGHVAR" (14 amino acids)

    • SMPP4: "DMYSDNLGLCDN" (12 amino acids)

    • SMPP7: "LYSLLTEK" (8 amino acids)

  Like other SMPs, SMPP3 is likely involved in biomineralization processes, but specific molecular functions remain to be characterized through further research.

Research Data and Technical Information

• What is known about the conservation of SMPP3 compared to other shell matrix proteins in Nautilus macromphalus?

  Comparative analysis of shell matrix proteins in Nautilus provides context for understanding SMPP3's conservation:

  Protein Type	Number Identified	Conservation Pattern	Reference
  Total shell-specific sequences	61	Nautilus-specific
  Successfully annotated sequences	27	Varying conservation
  Proteins with predicted domains	19	Some conserved across Conchiferans
  Proteins conserved in all 5 Conchiferans	3	Highly conserved
  Proteins shared among 4 marine Conchiferans	5	Marine-specific conservation
  Domains conserved in all 5 Conchiferans	6	Functionally significant
  Domains shared among 4 marine Conchiferans	6	Marine adaptation related

  The six domains conserved across all Conchiferans are A2M_comp, A2M_recep, Chitin-Binding Type 2 (ChtBD2), Signal peptide, Tyrosinase, and Von Willebrand factor type A (VWA) . Determining whether SMPP3 contains any of these domains would provide insights into its evolutionary conservation and potential functional role.

• How does the habitat of Nautilus macromphalus influence the study and interpretation of shell matrix proteins like SMPP3?

  The unique habitat and ecology of Nautilus macromphalus provide important context for studying SMPP3:

  1. Depth adaptation: Nautilus macromphalus specimens are typically captured at depths of approximately 400m off Nouméa, New Caledonia . This deep-water habitat subjects the shell to high pressure, which may influence the biomineralization process and the functional requirements of shell proteins.

  2. Isotopic evidence: Oxygen and carbon isotope analyses of Nautilus shells provide insights into their habitat depth and metabolic activity through ontogeny . These isotopic signatures reflect environmental conditions during shell formation and can be correlated with expression patterns of shell proteins.

  3. Evolutionary context: Nautilus represents one of the few extant cephalopods that retained an external biomineralized shell, while most modern cephalopods have internalized, reduced, or completely lost their shells . This evolutionary distinctiveness makes their shell proteins particularly interesting for comparative studies.

  4. Morphological considerations: Morphological parameters such as whorl expansion rate, whorl width index, and siphuncle position index change during ontogeny . These changes may correlate with differential expression of shell matrix proteins during development.

  5. Symbiotic relationships: Nautilus macromphalus harbors bacterial symbionts in its pericardial appendage, including a beta-proteobacterium and a coccoid spirochaete . While not directly related to shell formation, this symbiosis highlights the complex biology of this organism and potential interactions between different physiological systems.

  Understanding these ecological and evolutionary factors provides crucial context for interpreting the functional significance of SMPP3 and other shell matrix proteins in Nautilus macromphalus.

• What protocols are recommended for functional assays of recombinant SMPP3?

  For researchers investigating the functional properties of recombinant SMPP3, the following assay protocols are recommended:

  1. Calcium-binding assays:

     • 45Ca radioisotope binding: Incubate purified SMPP3 with 45Ca2+ and measure bound calcium through scintillation counting

     • Calcium colorimetric assays: Using calcium indicators like Arsenazo III or o-cresolphthalein complexone

     • Isothermal titration calorimetry (ITC): For quantitative measurement of binding thermodynamics

  2. In vitro mineralization assays:

     • Calcium carbonate crystallization: Monitor crystal formation in the presence/absence of SMPP3 using ammonium carbonate diffusion method

     • Crystal morphology analysis: Examine crystal habit, size, and polymorph using polarized light microscopy, SEM, and Raman spectroscopy

     • Growth rate measurements: Real-time observation of crystal growth using light microscopy or AFM

  3. Protein-protein interaction studies:

     • Pull-down assays with other shell matrix proteins

     • Surface plasmon resonance (SPR) for kinetic analysis of interactions

     • Yeast two-hybrid screening to identify potential binding partners

  4. Structural studies:

     • Circular dichroism (CD) to assess secondary structure in different conditions

     • Differential scanning calorimetry (DSC) to measure thermal stability

     • Size exclusion chromatography with multi-angle light scattering (SEC-MALS) to determine oligomeric state

  5. Cell culture assays:

     • Effects on mantle epithelial cells (if available) or other relevant cell types

     • Calcium uptake in cellular models

     • Extracellular matrix deposition in the presence of SMPP3

  When designing these experiments, it's important to include appropriate controls, such as heat-denatured SMPP3, other shell matrix proteins, and non-shell proteins of similar size/charge characteristics.