Proteins: Neglected active ingredients in edible bird’s nest

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TL;DR

This review identifies and summarizes seven key proteins in edible bird’s nest (EBN) that are frequently detected across proteomic studies, including acidic mammalian chitinase, lysyl oxidase homolog 3, mucin-5AC, ovoinhibitor, nucleobindin-2, calcium-binding protein (MW: 4.5 × 10^4), and glucose-regulated protein (MW: 7.8 × 10^4). The bioactivities of these proteins—such as immune regulation, anti-inflammatory effects, and tissue protection—closely align with the known health benefits of EBN, suggesting that proteins, rather than sialic acid alone, are the primary active ingredients. This review provides a foundation for future research linking specific EBN proteins to its therapeutic effects.

Full summary

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**Background:** Edible bird’s nest (EBN) is a traditional Asian invigorant, particularly valued in China, where it is consumed for its health benefits including immune regulation, anti-aging, and lung nourishment. Although sialic acid has been considered the main active component, proteins constitute 50%–67% of EBN’s total mass and have been largely overlooked. This narrative review aims to systematically catalog the proteins identified in EBN, describe their structures and bioactivities, and correlate these with EBN’s biological functions.

**Methods:** The authors conducted a literature review of proteomic studies on EBN, compiling a list of 58 proteins identified across multiple studies using techniques such as MALDI-TOF-MS, GPC, and RP-HPLC. They focused on seven proteins that were identified three or more times: acidic mammalian chitinase (AMCase), lysyl oxidase homolog 3 (LOXL3), mucin-5AC (MUC5AC), ovoinhibitor, nucleobindin-2 (NUCB2), calcium-binding protein (SDF4, MW: 4.5 × 10^4), and glucose-regulated protein (GRP78, MW: 7.8 × 10^4). For each, the authors summarized its source, structure, and known bioactivities from the literature.

**Key Results:** The seven main proteins and their bioactivities are: - **AMCase** (identified 9 times): Degrades chitin; has antiviral, anti-inflammatory, and anti-apoptotic effects; controls Th2 inflammatory response via IL-13; prevents pulmonary fibrosis; stimulates pulmonary epithelial cells to produce chemokines. - **LOXL3** (identified 6 times): Stabilizes fibrils and elastin; maintains blood vessel wall integrity; enhances integrin signaling; removes acetyl/acetamido groups from STAT3, aiding immune regulation; implicated in skin, cardiovascular, tendon, and immune health. - **MUC5AC** (identified 5 times): Forms protective gels in stomach, eyes, and airways; mediates bicarbonate gradient and bilayer mucus barrier with MUC6; captures foreign debris in tear fluid; prevents viral and parasitic infections. - **Ovoinhibitor** (identified 3 times): Serine protease inhibitor; antibacterial defense; prevents rotavirus antigen shedding; may cause IgE allergic reactions. - **NUCB2** (identified 3 times): Maintains calcium homeostasis; prevents insulin resistance; promotes cell proliferation; inhibits adipocyte differentiation; processed into nesfatin-1 to induce satiety. - **SDF4** (identified 3 times): Alleviates endoplasmic reticulum (ER) stress; regulates calcium-dependent activities in ER; essential for cellular calcium homeostasis. - **GRP78** (identified 3 times): Alleviates ER stress; anti-apoptotic; neuroprotective; prevents transport of misfolded proteins.

The authors note that these proteins collectively contribute to EBN’s immune regulation (via AMCase, LOXL3, SDF4, GRP78), skin health (LOXL3, NUCB2), gastric and pulmonary protection (AMCase, MUC5AC), and other effects.

**Clinical Implications:** This review highlights that proteins, not just sialic acid, are likely the key bioactive components of EBN. The identified proteins have well-documented roles in immune modulation, tissue protection, and metabolic regulation, which align with EBN’s traditional uses. However, the authors caution that the bioactivities of intact proteins may not persist after digestion; further pharmacological studies are needed to determine if digested peptides retain similar effects. Additionally, variability in EBN composition due to source, type, and season may affect protein profiles, and many proteins remain unidentified. This work provides a framework for future research to link specific EBN proteins to its therapeutic benefits and to explore potential applications in immune, gastrointestinal, and pulmonary health.