Question

What are the functions of marker proteins, transport proteins, and receptor proteins?

Answer 1

Marker/Recognition proteins extend across the cell membrane and serve to identify the cell. The immune system uses these proteins to tell good cells from foreign invaders. 

Answer 2

Marker proteins extend across the cell membrane and serve to identify the cell.The immune system uses these proteins to tell friendly cells from foreign invaders. They are as unique as fingerprints. They play an important role in organ transplants.

Source: protein sequencing

https://www.creative-proteomics.com/services/sequence-analysis-of-peptides-or-proteins.htm