GEM reconstruction protocol¶
This is a complete, worked example of reconstructing a genome-scale metabolic model (GEM) from homology, using RAVEN. It follows the published protocol:
Zorrilla F, Kerkhoven EJ (2022). Reconstruction of Genome-Scale Metabolic Model for Hansenula polymorpha Using RAVEN. In: Yeast Metabolic Engineering: Methods and Protocols, Methods in Molecular Biology vol. 2513, pp. 271–290. https://doi.org/10.1007/978-1-0716-2399-2_16
All scripts and data are hosted in the
hanpo-GEM repository, where
hanpo-GEM is a short name for the model. The complete, runnable version of
every command on these pages lives in
code/reconstructionProtocol.m;
the section numbering there matches the page titles here. The commands shown in
these pages are occasionally more concise than in the script (typically around
file locations).
What are genome-scale metabolic models?¶
Cellular metabolism is a complex network of hundreds to thousands of reactions
and metabolites. A GEM is a mathematical description of that network. At its core
is the stoichiometric matrix (S-matrix) of dimensions M × N, where M
is the number of metabolites and N the number of reactions. Each reaction is
bounded by a lower (LB) and upper (UB) bound reflecting thermodynamics and
reversibility, and gene–reaction associations are stored in grRules.
Constraining the model with measurable rates (such as carbon uptake) lets you estimate all intracellular fluxes by flux balance analysis (FBA), and so predict phenotypes — supporting applications from strain engineering to antibiotic discovery and microbial-community analysis.
The homology-based approach¶
RAVEN can create a draft GEM for an organism of interest by using well-curated models of phylogenetically related organisms as templates. Whether a given reaction from a template is included in the new model is decided by homology between the protein sequences of the two organisms (determined by bidirectional BLAST).
In this protocol a draft model is reconstructed for the industrially relevant methylotrophic yeast Hansenula polymorpha (also known as Ogataea polymorpha), which lacks a published high-quality GEM. Two highly curated yeast models are used as templates:
| Template | Organism | Role |
|---|---|---|
| yeast-GEM | Saccharomyces cerevisiae (ascomycete) | Primary template |
| rhto-GEM | Rhodotorula toruloides (basidiomycete) | Complementary template |
Same identifier namespace
When using multiple template models it is essential that they use the same identifiers for metabolites, reactions and compartments. The yeast-GEM and rhto-GEM models used here share the same identifier style.
Overview of the steps¶
The reconstruction proceeds through the following stages (each a page in this section):
- Materials and installation — software, files and verifying RAVEN.
- Import template models — load the yeast-GEM and rhto-GEM templates.
- Draft from homology — BLAST and
getModelFromHomology. - Biomass composition — DNA, RNA, protein, carbohydrate and lipid pseudoreactions.
- Curation of lipid reactions — the SLIME formalism.
- Gap-filling — make the draft able to produce biomass.
- Save and simulate — version control and FBA.
- Manual curation — fix gene associations, add methanol metabolism.
See Anticipated results for what the finished draft should look like.