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United States Patent 5,491,075: What Do the Claims Actually Cover?

US 5,491,075 claims a process and associated constructs for producing human α-N-acetylgalactosaminidase using mammalian-cell expression of an intra-frame fusion protein that can be captured via a binding domain (protein A domain E or an antigen recognized by specific immunoglobulin) and then cleaved at a defined junction (a collagenase substrate site) to release the target enzyme.

At a practical level, the patent tries to lock up a manufacturing workflow:

1) express a fusion (target enzyme linked N-terminally or C-terminally to a capture moiety via a site-specific cleavage junction),
2) purify via affinity capture (protein A domain E binders or antigen-specific antibodies),
3) perform enzymatic cleavage at the engineered site (collagenase substrate option),
4) recover the separated human α-N-acetylgalactosaminidase.

The claims also narrow to specific DNA coverage (SEQ ID NO:1) and a specific deposited vector (pAGB-3, accession B-18724) plus collagenase-site details.

Claim 1: Is This Really One Invention or Several?

Core claim structure

Claim 1 is a method with four steps:

(a) Cell culture and fusion expression
A mammalian cell contains a nucleotide sequence encoding a cleavage site “sandwiched” between:
- an α-N-acetylgalactosaminidase coding sequence
- and either (i) protein A domain E coding sequence
  The sequences are in the same translational reading frame. A second regulatory sequence controls expression so that the fusion protein is expressed.
(b) Recover fusion protein from the culture.
(c) Treat fusion protein with a substance that cleaves the cleavage site
Cleavage separates α-N-acetylgalactosaminidase from the binding protein.
(d) Recover separated α-N-acetylgalactosaminidase.

What this claim “locks”

Claim 1 locks the combination of:

human α-N-acetylgalactosaminidase expression in mammalian cells
in-frame fusion with a capture domain (Protein A domain E in the base claim)
a junction cleavable by an exogenous “substance”
post-expression cleavage used as a release step prior to recovery.

What it does not clearly lock

Claim 1 does not explicitly require:

any particular promoter/enhancer details beyond “second nucleotide sequence regulates gene expression”
any specific cleavage enzyme other than “a substance that cleaves the cleavage site”
any specific purification mechanics beyond “recover the fusion protein” and then cleave.

This breadth matters: the “substance” can be broadly interpreted as any cleavage agent matching the engineered junction. That keeps claim 1 active even if the capture step uses different immuno-affinity formats, as long as it still falls within the stated fusion design.

Do Claims 2 and 3 Create Meaningful Narrowing?

Claim 2: affinity capture via immunoglobulin binding partner

Claim 2 specifies recovery of the fusion protein by:

reacting the fusion protein with an immunoglobulin binding partner for protein A domain E.

This narrows claim 1 by tying capture to Protein A domain E’s known immunoglobulin-binding function. In real manufacturing terms, it implies an affinity resin or binding reagent that can bind protein A domain E.

Claim 3: immobilization

Claim 3 tightens further:

the immunoglobulin binding partner is immobilized.

That matters because immobilization can be used to distinguish from solution-phase binding in some infringement analyses. Still, claim 3 does not specify resin chemistry, linker strategy, or antibody species, leaving operational latitude.

Claim 4: Does the pAGB-3 Deposit Add Real Enforceability?

Claim 4 limits the method (claim 1 dependent) to:

recombinant vector pAGB-3
deposited with ATCC (Agricultural Research Culture Collection) under B-18724.

A deposit-anchored claim is often more enforceable against parties using the exact deposit plasmid or near-identical variants, but it is also narrower in coverage: method infringement for teams using a different plasmid (even if they reproduce the same protein architecture) may fail if their construct differs materially from pAGB-3.

This claim also signals that the patent’s enablement and specific DNA coverage is not theoretical; it is tied to an actual deposited construct.

Claim 5-6: Is the “Antigen” Version a Different Invention?

Claim 5: swap Protein A domain E for an antigen

Claim 5 mirrors claim 1 but replaces:

protein A domain E with a protein antigen coding sequence.

It requires:

in-frame fusion with a cleavage site between α-N-acetylgalactosaminidase and the protein antigen
recovery of fusion by reaction with an immunoglobulin directed against the protein antigen
cleavage treatment to release α-N-acetylgalactosaminidase
recovery of separated enzyme.

Claim 6: immobilized immunoglobulin

Claim 6 requires:

the immunoglobulin is immobilized.

Operationally, claim 5-6 expands the affinity-capture concept from protein A to any antigen paired with a corresponding immunoglobulin, as long as the antigen is encoded in the fusion and the immobilized antibody captures the fusion protein.

This broader “capture-by-antigen” frame is a classic posturing move: it can cover multiple antigen-antibody systems while staying within the same cleavage-junction release architecture.

Claim 7-8: The Collagenase Cleavage Option Is a Key Pivot

Claim 7: cleavage is enzyme + substrate-specific cleavage site

Claim 7 requires:

the cleavage “substance” is an enzyme
cleavage site is a substrate specific for the enzyme.

This is a technical tightening that implies the junction is not just chemically cleavable; it is engineered to be enzymatically processed.

Claim 8: collagenase

Claim 8 specifies:

the enzyme is collagenase.

This is the most commercially salient narrowing element. Many competitors can implement generic protease cleavage junctions, but collagenase-specific cleavage motifs are more constrained. If competitors use a different protease (e.g., TEV, Factor Xa, thrombin, engineered proteases), they may avoid the collagenase-substrate requirement while still doing affinity capture and cleavage generally.

Claims 9-10: SEQ ID NO:1 Tightens the DNA Landscape

Claim 9

α-N-acetylgalactosaminidase coding sequence comprises SEQ ID NO:1 “depicted in FIG. 2” from nucleotide 1 to 1236.

Claim 10

SEQ ID NO:1 from nucleotide 52 to 1236.

These claims try to capture:

a full coding region coverage (or start-inclusive form)
a shortened version that still represents the key coding region.

From a landscape standpoint, SEQ ID NO:1-based limitations can be used to argue non-infringement if an accused DNA sequence differs materially from SEQ ID NO:1 while still producing functional enzyme. Conversely, parties using the same or extremely similar sequence architecture may face direct claim read.

Claims 11-15: What Product-By-Process Claim Coverage Looks Like Here

Claim 11: recombinant vector (fusion architecture)

Claim 11 claims:

a recombinant vector comprising:
- nucleotide sequence encoding a cleavage site
- sandwiched between α-N-acetylgalactosaminidase coding sequence and protein A domain E coding sequence
- in same reading frame
- controlled by nucleotide sequence regulating fusion expression in mammalian host cell.

This is a structural claim on the genetic construct.

Claim 12: recombinant vector pAGB-3

Claim 12 mirrors claim 4 at the vector level:

recombinant vector pAGB-3 deposited as B-18724.

This is the tightest enforceability hook if someone uses that deposit plasmid.

Claim 13: antigen version

Claim 13 claims the antigen-fusion vector:

cleavage site between α-N-acetylgalactosaminidase and protein antigen coding sequence
in-frame
mammalian expression control.

Claim 14: selectable marker

Claim 14 adds:

vector includes a selectable marker.

This is usually hard to avoid because most expression vectors carry selectable markers (ampicillin/neo blasticidin etc.), but the claim only applies to vectors of claim 11 or 13.

Claim 15: cleavage site is collagenase substrate

Claim 15 locks the cleavage biology:

cleavage site is a collagenase substrate.

In vector terms, claim 15 is a direct DNA-level narrowing for competitors. If the junction sequence is not a collagenase substrate, it is not within claim 15.

Critical Take: The Claim Set Is a “Manufacturing Scaffold” With Narrow Enzymatic Specificity

Where the patent is broad

Claims 1 and 5 broadly cover:
- mammalian-cell expression of α-N-acetylgalactosaminidase fusion proteins
- affinity capture via either Protein A domain E or an antigen-antibody system
- cleavage at an engineered junction by any cleaving substance (until claims 7-8 narrow it).

Where it is narrow

Collagenase specificity (claims 7-8, 15) is a meaningful constraint.
SEQ ID NO:1 limitations (claims 9-10) are another meaningful constraint.
pAGB-3 deposit (claims 4 and 12) is a narrow, copy-target restriction.

Where it is strategically ambiguous

The claims say “cleavage site sandwiched between … arranged in the same translational reading frame.” They do not define:
- the exact N- vs C-terminal orientation of the fusion
- whether “sandwiched” means direct junction or spacer
- exact collagenase substrate motif sequence boundaries. If a competitor uses an in-frame fusion with a different junction sequence that still yields cleavage, infringement will depend on claim construction of “cleavage site” and substrate specificity.

Patent Landscape Implications (US 5,491,075 as the Anchor)

Landscape signals from the claim content

The claim strategy reflects three common industry design choices that can be cross-compared against other patent families:

1) Fusion-mediated purification
Protein A domains and antigen-antibody affinity capture are common purification tactics in mammalian expression systems. This patent’s novelty likely lies in the specific fusion architecture with α-N-acetylgalactosaminidase and the engineered cleavage junction.

2) Site-specific enzymatic release
Collagenase substrate specificity is uncommon relative to widely used protease recognition sites. Competitors seeking freedom-to-operate often pick TEV/Factor Xa/thrombin or chemically cleavable linkers. Collagenase-directed cleavage is a differentiator.

3) DNA sequence anchoring
SEQ ID NO:1 and pAGB-3 deposit indicate the patent owner sought to claim real biological implementations rather than abstract concepts.

Actionable reading for R&D or licensing

If a development program uses mammalian expression plus fusion capture and cleavage release, it should map whether:
- the capture domain is Protein A domain E or an antigen
- the cleavage enzyme is collagenase
- the engineered junction is a collagenase substrate
- the coding sequence aligns with SEQ ID NO:1 and the vector resembles pAGB-3.

This is the core infringement surface.

Claim Coverage Matrix (How Each Dependent Claim Modifies Risk)

Claim	Key technical restriction	Main effect on claim scope
1	Mammalian expression of α-N-acetylgalactosaminidase fusion with Protein A domain E via in-frame cleavage site; recover; cleave; recover enzyme	Establishes the base scaffold; cleavage “substance” broad until later claims
2	Fusion recovery uses immunoglobulin binding partner for protein A domain E	Narrows capture mechanics to Protein A-typical binders
3	Binding partner is immobilized	Narrows to immobilized affinity capture
4	Vector limited to pAGB-3 (deposit B-18724)	Narrowest at method level; strongest for copy-plasmid risk
5	Same scaffold but capture is via protein antigen and immunoglobulin directed to it	Expands beyond protein A to antigen-antibody systems
6	Immunoglobulin is immobilized	Nests into fixed affinity capture formats
7	Cleavage substance is enzyme; cleavage site is enzyme substrate specific	Converts generic cleavage into substrate-driven enzymatic cleavage
8	Enzyme is collagenase	Major narrowing; competitors can design around by using other protease systems
9	α-N-acetylgalactosaminidase coding sequence equals SEQ ID NO:1 (nucleotide 1-1236)	Narrows DNA identity
10	Coding sequence equals SEQ ID NO:1 (nucleotide 52-1236)	Captures an alternate start/variant of SEQ ID NO:1
11	Vector claim for Protein A domain E fusion architecture	Enables product-side enforcement (construct-based)
12	Vector limited to pAGB-3 (B-18724)	Tightest vector-level restriction
13	Vector claim for antigen fusion architecture	Captures antigen-antibody fusion vectors
14	Vector includes selectable marker	Minor practical narrowing
15	Cleavage site is collagenase substrate	Key vector-level design-around point

Key Takeaways

US 5,491,075 claims a mammalian-cell fusion expression approach for producing human α-N-acetylgalactosaminidase, using affinity capture (Protein A domain E or an antigen recognized by immunoglobulin) followed by cleavage at an engineered junction and then enzyme recovery.
The enforcement surface is driven by four design parameters: (i) fusion capture domain (Protein A domain E vs antigen), (ii) in-frame cleavage junction, (iii) whether the cleavage is collagenase-specific, and (iv) whether the construct matches SEQ ID NO:1 or the deposited vector pAGB-3 (B-18724).
The most important design-around lever for competitors is not the affinity capture method alone; it is the collagenase substrate cleavage junction and the specific DNA/construct constraints (SEQ ID NO:1 and pAGB-3).

FAQs

1) Is the patent limited to Protein A domain E?

No. The base method claim uses Protein A domain E (claim 1), but the patent also claims an antigen-based capture alternative (claims 5, 6, and corresponding vector claims 13).

2) What is the most significant narrowing element in the claim set?

Collagenase cleavage. Claims 7-8 and 15 require collagenase (or, at minimum, that the cleavage site is a collagenase substrate in the vector claim).

3) Does the patent cover any mammalian expression of α-N-acetylgalactosaminidase?

No. Coverage hinges on an in-frame fusion that includes a cleavage site and a capture domain (Protein A domain E or an antigen) and a release step using a cleaving substance, with collagenase required in the narrower dependent claims.

4) How does SEQ ID NO:1 affect infringement risk?

Claims 9-10 restrict the α-N-acetylgalactosaminidase coding sequence to specific nucleotide ranges of SEQ ID NO:1, limiting coverage for constructs that encode the same enzyme via different sequences.

5) Why do the pAGB-3 deposit claims matter?

Claims 4 and 12 tie the scope to a specific deposited vector (B-18724). Using that deposited plasmid increases direct alignment with the narrowest method/vector claims.

References

[1] U.S. Patent 5,491,075.

Applicant	Tradename	Biologic Ingredient	Dosage Form	BLA	Approval Date	Patent No.	Expiredate
Smith & Nephew, Inc.	SANTYL	collagenase	Ointment	101995	June 04, 1965	⤷ Start Trial	2014-06-17
Genzyme Corporation	FABRAZYME	agalsidase beta	For Injection	103979	April 24, 2003	⤷ Start Trial	2014-06-17
Genzyme Corporation	FABRAZYME	agalsidase beta	For Injection	103979	October 10, 2003	⤷ Start Trial	2014-06-17
>Applicant	>Tradename	>Biologic Ingredient	>Dosage Form	>BLA	>Approval Date	>Patent No.	>Expiredate

Summary for Patent: 5,491,075