I've used PSIPRED to to attain the secondary structure of particular integral membrane protein. There are long stretches of Alpha Helices and there are certain beta strands which are linked to those alpha helices. I've read that that the long stretches of alpha-helices are most possibly internal transmembrane regions. The extended strands or beta sheets linked to the alpha-helices may act as beta-barrels, and thus construct the external transmembrane regions of the protein (this is paraphrased)
I need research papers to support this claim. I cannot seem to remember where I've read it. I have attached an image in the description. If anyone can kindly provide me with scientific papers where they claim this, then it would of great help. My statement might be wrong, if so then please clarify it for me. Thank you.