US 7,445,775: What the Microplasminogen-Yeast Claims Actually Cover and Where the Landscape Turns
United States Patent 7,445,775 centers on producing microplasminogen (a pro-enzyme form) using yeast engineered to express a defined mammalian-sequence construct that encodes an exact microplasminogen amino-acid sequence (SEQ ID NO: 4), with specific production parameters (inducible expression, secretion signal fusions, genome integration, and deposition-defined strain usage) and downstream conversion to activated microplasmin via a plasminogen activator such as staphylokinase, followed by stabilization (lysine, 6-aminohexanoic acid, tranexamic acid; acid media such as citrate buffer at about pH 3.1), and optional drying.
From an infringement and freedom-to-operate (FTO) perspective, the claim set is built as a “stack” of narrow anchor features:
- The protein is fixed by sequence definition (SEQ ID NO: 4).
- The DNA is fixed by nucleotide definition (SEQ ID NO: 3).
- The production system is constrained to methylotrophic yeast, commonly Pichia pastoris, often with an identified deposited strain (MUCL43676).
- The activation step is constrained to a plasminogen activator, with staphylokinase called out.
- The stabilization/drying media are specified with concrete chemical options and citrate buffer (pH ~3.1).
That architecture narrows enforceable scope but also creates many “design-around” degrees of freedom for parties who do not want to litigate sequence-level boundaries and yeast-strain-specific deposition constraints.
What do the key claims require, in operational terms?
1) Claims 1-11: Yeast cell expressing defined microplasminogen
Independent claim 1 defines the invention as a yeast cell expressing microplasminogen with:
- Microplasminogen amino acid sequence = SEQ ID NO: 4 (absolute sequence lock)
- Mammalian nucleotide sequence encodes the microplasminogen
- The yeast cell includes at least one mammalian nucleic acid construct matching the described encoding
The dependent chain tightens this in multiple directions:
| Claim |
Added requirement (material constraint) |
| 2 |
Mammalian nucleotide sequence is SEQ ID NO: 3 |
| 3 |
Mammalian sequence is under an inducible promoter |
| 4 |
Yeast is methylotrophic |
| 5 |
Yeast genus limited: Hansenula, Pichia, Candida, Torulopsis |
| 6 |
Species limited to Pichia pastoris |
| 7 |
Mammalian nucleotide integrated into yeast genome |
| 8 |
Yeast cell is the deposited strain MUCL43676 |
| 9 |
Expression level of microplasminogen at least ~100 mg/L |
| 10 |
Mammalian sequence is fused to a nucleotide encoding a secretion signal |
| 11 |
A second independent form: yeast cell expressing microplasminogen with SEQ ID NO: 4 |
Practical read-through: the enforceable sweet spot is not just “yeast expresses microplasminogen.” It is “yeast expresses the exact pro-enzyme defined by SEQ ID NO: 4 using a defined mammalian encoding (SEQ ID NO: 3), often with secretion targeting and induction controls, often with integration and strain identity.”
2) Claims 12-23: Method producing activated microplasmin
Independent claim 12 requires a multi-step production pipeline:
(a) Provide a yeast cell transformed with nucleotide encoding microplasminogen amino acid sequence SEQ ID NO: 4
(b) Culture under conditions so that microplasminogen is expressed
(c) Activate the microplasminogen using a plasminogen activator
Dependent claims specify activator choice and stabilization:
| Claim |
Added requirement |
| 13 |
Plasminogen activator is staphylokinase |
| 14 |
Stabilize expressed and activated microplasmin using stabilizing agent or medium |
| 15 |
Stabilizing agent is amino acid from: lysine, 6-aminohexanoic acid, tranexamic acid |
| 16 |
Stabilizing medium is an acid solution or acid buffer |
| 17 |
Stabilizing medium is citrate buffer pH ~3.1 |
| 18 |
Dry expressed, activated, stabilized microplasmin |
| 19 |
Recombinant mammalian protein obtained by method of claim 12 |
| 20 |
Yeast transformed with SEQ ID NO: 3 and a high expression Pichia strain selected |
| 21 |
Optional purification step by one or more purification methods |
| 22 |
Yeast cell is deposited strain MUCL43676 |
| 23 |
Microplasminogen expressed at about 100 mg/L |
Practical read-through: the claim is both biological (yeast expression of the exact sequence) and chemical-process constrained (activation, then stabilization in specific chemical classes, and optional drying). If a competing process uses different activation machinery or stabilization chemistry, it can avoid large parts of the claim set even if it expresses the same sequence.
3) Claims 24-30: Nucleic acid, vector, cells, and purified microplasminogen
This block is built as standard patent scaffolding around the fixed protein sequence:
- Isolated nucleotide encoding fusion of microplasminogen + secretion signal
- Nucleotide containing SEQ ID NO: 3
- Isolated cell containing nucleic acid
- Isolated vector containing nucleic acid
- Isolated cell containing vector
- Purified microplasminogen (SEQ ID NO: 4)
- Isolated cell producing microplasminogen
Practical read-through: These claims let the patentee capture upstream and product forms even if the defendant does not use the exact “method” wording. But again, the fixed-sequence requirement is the central boundary.
4) Claims 31-32: Pharmaceutical compositions
- Pharmaceutical composition comprising microplasminogen (SEQ ID NO: 4)
- Further comprising a pharmaceutically-acceptable carrier
Practical read-through: Composition claims are often broad in formulation but narrow in active identity. Here, the active ingredient identity is sequence-locked.
How is this patent likely to behave in enforcement: infringement trigger points vs attack points
Where infringement is easiest (stronger trigger points)
-
Exact sequence match
Any competitor producing microplasminogen whose amino acid sequence is SEQ ID NO: 4 will be pulled into the highest-risk lane, even if yeast species or promoter details change, depending on which claims are asserted.
-
Secretion signal fusion
Claims involving nucleic acid/vector/cell products explicitly recite a fusion to a secretion signal sequence. If the competitor uses secretion addressing, the scope can widen. If it does not, those particular claims become harder for the patentee.
-
Activation chemistry and stabilizer stack
If a competitor uses staphylokinase and the stabilization stack includes lysine/6-aminohexanoic acid/tranexamic acid or acidic media such as citrate buffer near pH 3.1, claim 12’s method chain is materially closer.
-
Deposited strain MUCL43676
Deposition-based claims can be powerful in court because “identity of the organism/cell line” is often objective. Defendants can reduce risk by using different strains.
Where defendants typically attack (narrowing defenses)
-
Sequence definition as a hard boundary
If microplasminogen differs by even small amino acid changes (or the construct yields a different processed form), the patentee’s core sequence-locked language becomes harder to map.
-
DNA identity boundary (SEQ ID NO: 3)
Many dependent claims anchor on “mammalian nucleotide sequence of SEQ ID NO: 3.” A competitor using alternative coding (synonymous codons do not always preserve “nucleotide sequence” identity in strict claim terms) can attempt non-infringement.
-
Yeast category and strain constraints
The methylotrophic yeast requirement is a category limiter. Moving outside methylotrophic systems (or using yeast that is not covered) can cut off claims that require that feature. Deposition identity (MUCL43676) offers another concrete carve-out.
-
Activation and stabilization route
The stabilization requirements are chemically specific. Using different activators or stabilizers can create a clean non-infringement path for method claims even when the biological production of microplasminogen is similar.
Claim-by-claim “risk map” for a generic competitor designing around
Biology and expression
- High risk: yeast expressing microplasminogen with SEQ ID NO: 4 under an inducible promoter, often in methylotrophic yeast such as Pichia pastoris, especially when integrated and/or using secretion signal fusions.
- Medium risk: same protein sequence, but not using inducible promoter, not methylotrophic yeast, or not using secretion signal fusion (depends which dependent claims are asserted).
- Lower risk: different microplasminogen amino acid sequence (not SEQ ID NO: 4), or different processing that yields a different amino-acid identity.
Activation
- High risk: activation using staphylokinase.
- Medium risk: other plasminogen activators not recited; the core method claim 12 still requires “a plasminogen activator,” so the defendant must still show its process does not meet the claim mapping if the activator falls within “plasminogen activator” broadly interpreted.
- Lower risk: no plasminogen activation step or activation path that does not fall within claim language.
Stabilization and drying
- High risk: lysine/6-aminohexanoic acid/tranexamic acid stabilizers; acid media such as citrate buffer pH ~3.1; drying after stabilization.
- Lower risk: different stabilization systems or non-acid stabilization conditions that do not meet claim-specific selections.
Product forms
- High risk: pharmaceutical compositions where active is microplasminogen of SEQ ID NO: 4.
- Lower risk: formulations that do not use microplasminogen matching the sequence.
Where the patent landscape pressure concentrates (portfolio logic)
This patent behaves like a “process + product identity” lock
Most of the patent’s value comes from the combination of:
- Defined protein identity (SEQ ID NO: 4)
- Defined DNA identity in some dependents (SEQ ID NO: 3)
- Defined host category and common industrial platform (methylotrophic yeast, Pichia pastoris)
- Defined activation and stabilization chemistry
That combination reduces the number of safe substitutions available to a developer who wants to make activated microplasmin at scale while keeping the same microplasminogen prodrug identity.
But it also leaves escape routes
The claim set does not read as a blanket monopoly over:
- All yeast-based plasminogen activation
- All forms of microplasmin (the sequence anchor is still required in many claims)
- All formulations of activated microplasmin with stabilizers outside the stated selections
- All activators other than the explicitly called-out staphylokinase for dependent claim 13
So the landscape risk is more concentrated around developers who:
- Keep the same pro-enzyme identity and
- Use a closely aligned yeast platform and
- Use a closely aligned activation and stabilization package.
Key takeaways
- The core infringement boundary is sequence identity: microplasminogen must match SEQ ID NO: 4; DNA identity (SEQ ID NO: 3) tightens in dependents.
- The host platform is constrained: claims repeatedly require methylotrophic yeast, often Pichia pastoris, and two dependents require deposited strain MUCL43676.
- Method claims hinge on downstream chemistry: activation by a plasminogen activator (with staphylokinase specified in claim 13) plus stabilization using selected amino acids or acid media such as citrate buffer at pH ~3.1, with an optional drying step.
- Design-around opportunities exist but are specific: avoid the sequence identity, switch away from the deposited strain, use different activator/stabilizer systems, and/or avoid secretion-signal fusions where those dependent claims matter.
FAQs
1. What is the single most important technical requirement in US 7,445,775?
The microplasminogen amino acid sequence must equal SEQ ID NO: 4 across the claim set that defines the active and its encoded constructs.
2. Does the patent cover yeast expression alone?
Yes for the yeast cell product claims, but the method and downstream product claims add constraints on activation and stabilization/drying.
3. How do MUCL43676-related claims change risk?
They narrow parts of the scope to a specific deposited strain. Using a different deposited line can reduce mapping to those dependent claims.
4. If a competitor uses a different activator than staphylokinase, is it automatically outside the patent?
It may avoid dependent claim 13, but claim 12 still requires activation “by means of a plasminogen activator,” so non-infringement depends on the activator and full claim mapping.
5. Are pharmaceutical composition claims broader than method claims?
They are broader in formulation mechanics (carrier language) but narrow in active identity: the composition must contain microplasminogen with SEQ ID NO: 4.
References (APA)
[1] United States Patent No. 7,445,775. Claims 1-32 (as provided in the prompt).
