Serum amyloid A-1 protein (SAA1)

Function
Serum amyloid A (SAA) proteins function as cytokine-like proteins with roles in the acute phase response, lipid transport and metabolism, cell-cell communication, atherosclerosis, and feedback in inflammatory, neoplastic, immunologic, and protective pathways¹. SAA proteins are normally found at low levels in healthy individuals, but after the onset of the acute phase response, SAA levels can increase by 1000-fold within 24 hours, with levels decreasing back to normal when the event resolves. However, elevated levels of SAA can persist when inflammation is chronic. Acute-phase SAA is tightly bound to high-density lipoprotein (HDL) and functions as an apolipoprotein.

Mechanism and pathways
The human genome encodes four major variants of SAA (SAA1-4), with Saa3 being a transcribed pseudogene¹. SAA1 and SAA2 are involved in the classic acute phase response and are synthesized and secreted by the liver (hepatocytes), macrophages, adipocytes, kidney, lung, and mammary gland cells. Transcription of Saa1 and Saa2 is also observed in synovial and brain cells. During the acute phase response, SAA1 expression is regulated by many transcription factors (NF-κB, C/EBP, YY1, AP-2, SAF, Sp1, STAT3), proinflammatory cytokines (IL-1β, IL-6, TNF-α), and glucocorticoids². SAA4 is constitutively expressed¹.

SAA1 is a major precursor of amyloid A and is known to form pathogenic amyloid fibrils when over-produced or aberrantly processed². Additionally, SAA1 is used as a clinical biomarker for inflammatory disorders² and may be useful as a prognostic marker in the tumor microenvironment³ or for metastasis of hepatocellular⁴ and renal cell⁵carcinomas. Additionally, SAA1 has been suggested as a novel therapeutic target of pancreatic cancer⁶.

Structure
Mature SAA1 protein consists of 104 amino acids and is a hexamer stabilized by its C-terminal tail². SAA proteins are poorly soluble in aqueous solutions, and concentrations needed to characterize their 3D structure are difficult to acquire¹. Heparin sulfate disrupts SAA binding to HDL.

Human

P0DJI8

MRSFFSFLGEAFDGARDMWRAYSDMREANYIGSDKYFHARGNYDAAKRGPGGVWAAEAISDARENIQRFFGHGAEDSLADQAANEWGRSGKDPNHFRPAGLPEKY

Lyophilized

~15k

~12k

Reconstitute at 0.1-1 mg/ml using filtered deionized water. Gently mix by vortexing and/or inversion until fully dissolved. Centrifuge if necessary.

This lyophilized protein is stable for twelve months when stored at -20°C to -70°C. After aseptic reconstitution, this protein may be stored for one month at 2°C to 8°C or for three months at -20°C to -70°C in a manual defrost freezer. Avoid Repeated Freeze Thaw Cycles.

Frozen Dry Ice

Human

Research Use Only

1 Sack GH Jr. Mol Med. 24(1):46. 2018.
2 Sun L, Ye RD. Gene. 583(1):48-57. 2016.
3 Xu Z, Wu Y, Fu G, et al. Int J Mol Sci. 24(8):7505. 2023.
4 Li G, Shen Q, Xu H, et al. Front Oncol. 13:1138995. 2023.
5 Li S, Cheng Y, Cheng G, et al. Front Oncol. 11:649761. 2021.
6 Takehara M, Sato Y, Kimura T, et al. Cancer Sci. 111(8):2883-2894. 2020.
7 Jiang B, Wang D, Hu Y, et al. Mol Metab. 59:101462. 2022.
8 Cao K, Jiang X, Wang B, et al. Front Neurol. 13:905561. 2022.
9 Bang YJ, Hu Z, Li Y, et al. Science. 373(6561):eabf9232. 2021.
10 Lee JY, Hall JA, Kroehling L, et al. Cell. 180(1):79-91. 2020.