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recombinant FGF2-G3 protein (Qk053)

FGF2-G3 (FGF2-STAB®) protein is a thermostable engineered form of FGF-2 (bFGF). Qk053 is the 154 aa mature domain of FGF-2 (Qk027) with nine amino acid substitutions to enhance stability without impacting bioactivity developed by Dvorak et al. 2018. This increases the functional half-life of the protein from <10 h (wild-type) to >7 days (FGF2-G3).

FGF2-G3 is used in B8 media (Kuo et al. 2019) for weekend free, high homogeneity induced pluripotent stem cell culture. FGF2-G3 also has applications in chemically defined stem cell and organoid culture media, and cultured meat media development.

High purity 17 kDa bioactive FGF2-G3 protein. Animal-free (AOF), carrier protein-free and with no His-tag.

Orders are typically shipped same or next day (except Friday).
Easy world-wide ordering, direct or through our distributors.


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enquiries, bulk and stock reservation, please email

1mg may be despatched as 2 x 500µg


  • high purity thermostable FGF2-G3 protein comprising 154 aa form of FGF-2 (Uniprot: P09038) with nine stabilizing amino acid substitutions 

  • 17 kDa

  • expressed in E. coli. 

  • animal-free (AOF) and carrier protein-free.

  • manufactured in our Cambridge, UK laboratories

  • frozen in PBS, 1mg/ml

  • prepare single use aliquots, add carrier protein if desired, store frozen at -20 oC or -80 oC
handling and storage FAQ

featured applications

  • expansion of induced pluripotent, embryonic and mesenchymal stem cells

  • cell expansion

Basic fibroblast growth factor, bFGF, FGF-β, FGF2, Fibroblast growth factor-basic, HBGF-2, FGF2-G3, FGF2-STAB, FGF2-STAB2

species neutral


FGF-2 (154 aa) (Qk027): wild-type form of this protein
FGF-G3 (145 aa) (Qk052): 145 aa form of  hyperstable FGF2-G3
FGF-2 145 aa (Qk025)
zebrafish FGF2 (Qk002)


Human LIF Qk036 protein bioactivity lot #14293

FGF2-G3 activity is determined using the Promega serum response element luciferase reporter assay (*) in transfected HEK293T cells. EC50 = 90 pg/ml (5.2 pM).

Cells are treated in triplicate with a serial dilution of FGF2-G3 for 3 hours. Firefly luciferase activity is measured and normalized to the control Renilla luciferase activity. Data from Qk053 lot #104340.

*Promega pGL4.33[luc2P/SRE/Hygro] #E1340


Human LIF Qk036 protein purity SDS-PAGE lot #14293

FGF2-G3 migrates as a major band at 17 kDa in non-reducing (NR) conditions.  The higher molecular weight minor band is the dimeric form.   Upon reduction (R), only the 17 kDa band is visible.  No contaminating protein bands are present.

Purified recombinant protein (3 µg) was resolved using 15% w/v SDS-PAGE in reduced (+β-mercaptothanol, R) and non-reduced (NR) conditions and stained with Coomassie Brilliant Blue R250.  Data from Qk053 batch #104340.

further quality assays

  • mass spectrometry: single species with expected mass

  • analytical reversed-phase: single sharp peak 

  • endotoxin: <0.005 EU/μg protein (below level of detection)

  • recovery from stock vial >95%

request CoA/animal-free certificate
download MSDS

We are a company founded and run by scientists to support innovation in stem cell biology and regenerative medicine.  To enhance reliability and reproducibility in your applications, all our products are exceptionally high purity, with complete characterisation and bioactivity analysis on every lot.

Wild-type FGF-2 and FGF2-G3 have equivalent bioactivity

FGF2-G3 activity is determined using the Promega serum response element luciferase reporter assay (*) in transfected HEK293T cells.
Cells are treated in triplicate with a serial dilution of FGF2-G3 for 3 hours. Firefly luciferase activity is measured and normalized to the control Renilla luciferase activity.

*Promega pGL4.33[luc2P/SRE/Hygro] #E1340

‘After a long day running samples and analysing data, it was very exciting to see just how stable the FGF2-G3 proteins were. They clearly have more endurance than me!’ – Kerry, Qkine Senior Scientist

Hyperstable FGF2-G3 retains activity after pre-incubation with conditioned media at 37 oC

+24 hours
+48 hours
+ 72 hours

FGF2-G3 (Qk053)            WT FGF2 (Qk027)

WT FGF-2 (Qk027)  and FGF2-G3 (Qk053) were diluted in conditioned media and incubated at 37oC. Samples were taken at 24 h intervals and FGF-2 activity was assayed in triplicate using the Promega serum response element luciferase reporter assay (*) in transfected HEK293T cells. Firefly luciferase activity was normalized to the control Renilla luciferase activity (F/R).

FGF2-G3 protein background

the history of FGF-2 and stem cell culture

FGF-2 (also known as basic FGF or bFGF) is an essential growth factor for maintaining human embryonic stem cell (hESC) and induced pluripotency stem cell (iPSC) pluripotency in feeder-free and chemically defined stem cell media. It is a core component of widely adopted media including mTESR (Ludwig et al. 2006), StemPRO (Wang et al. 2007) and E8  (Chen et al. 2011). However, FGF-2 is inherently unstable and prone to proteolytic degradation and aggregation. This fundamental biochemical instability, and therefore low half-life in culture media (<10 h), is an important contribution to the need for frequent media changes and challenges in improving homogeneity during stem cell proliferation and subsequent differentiation.

To improve the stability of FGF-2 for stem cell media and regenerative medicine applications, Dvorak and colleagues at Masaryk University used computer-assisted protein engineering to identify an optimal set of nine amino acid substitutions that stabilize FGF-2. These substitutions were designed to avoid structural changes to the FGF receptor 1 (FGFR1) and FGF receptor 2 (FGFR2) binding interface. This thermostable FGF-2 is known as FGF2-G3, or FGF2-STAB® (Dvorak et al. 2017). The biological activity of wild-type FGF-2 is <50% after 10h incubation with conditioned media. In contrast, no reduction in FGF2-G3 biological activity is observed after >7 days incubation with conditioned media at 37oC. Both FGF2-G3 and wild-type FGF-2 maintain hESC pluripotency and expression of pluripotency markers Oct-4 and nanog with equivalent efficacy (Dvorak et al. 2017).

In 2020, Paul Burridge and colleagues at Northwestern University, Chicago, published a protocol for B8 media. This iPSC maintenance media uses thermostable FGF2-G3, along with optimization of media component concentration and composition to reduce media cost and facilitate weekend-free stem cell culture regimes (Kuo et al. 2020 and updated in Lyra-Leite et al. 2020).

To manufacture and provide FGF2-G3 for stem cell culture, including use in B8 media and emerging applications such as cellular agriculture, Qkine has licensed the patented FGF2-G3 technology from Enantis/Masaryk University.  We have combined the excellent science behind the FGF2-G3 technology with our protein manufacture expertise to provide gold standard protein for use in cell culture media. We have removed His tags present in the academic forms of the protein for FGF2-G3 (Qk053), as these may cause issues for scientists looking to translate discoveries to clinical or scale-up applications, and introduce unnecessary scientific uncertainties.

Two forms of FGF-2 are used frequently in stem cell culture: 145 aa Qk025 and 154 aa (Qk027).

The 9 aa pro-segment of FGF2 present in the 154 aa FGF-2 is not required for biological activity and is thought to have roles in the localization of FGF-2 in vivo.
We wanted to allow scientists to compare directly with their existing FGF-2, so we introduced the nine amino acid substitutions into the 145 aa form of FGF-2 to make Qk052 FGF2-G3 (145 aa). The EC50 of the two forms of FGF2-G3 are 90 pg/ml and 47 pg/ml for the 154 aa and 145 aa forms respectively.  As observed previously, the half-life is extended to >3 days.

key papers

Dvorak et al. 2018

development of FGF2-G3 form using AI

Koledova et al. 2019

assessment of FGF2-G3 stability and signalling

Kuo et al. 2020

development of B8 media – low cost, weekend free iPSC media

Lyra-Leite et al. 2021

updated protocol for B8 media

Benington et al. 2020

nice review of FGF2 stability and stabilisation methods

Our products are for research use only and not for diagnostic or therapeutic use.  Products are not for resale.

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