Hacker News Reader

Comment by newsocks | Hacker News Reader

How are miniproteins any different than just peptides?

The article references "miniproteins"as being the same as "minipetides"... as though these are both different from regular peptides.

Wikipedia states that peptides are "approximately 50 or fewer amino acids" [0] while minipeptides are "a length of less than 100-150 amino acids" [1].

Is this article really just saying that "peptides are upending cell biology"?

[0] https://en.wikipedia.org/wiki/Peptide [1] https://en.wikipedia.org/wiki/Micropeptide

View on HN

The difference is that the peptides are generated by chopping up larger proteins, while miniproteins are synthesised as short proteins. I.e. you need other enzymes to turn a protein into peptide, but a microprotein only needs to be translated to be short!

The boundary between 'peptide' and 'protein' is a little fuzzy. There are 'small proteins' like:

https://en.m.wikipedia.org/wiki/Thionin

that are 45-48 amino acids which is less than the (arbitrary) lower limit of 50.

One distinguishing feature of a protein is that it folds, while peptides usually are too short to have a defined fold.

> while peptides usually are too short to have a defined fold.

That's not strictly true. My PhD project has looked at an entire class of peptides that are known to fold in to alpha-helices when bound to a cell membrane e.g. https://www.rcsb.org/structure/2k9b.

There are many others that are known to fold into beta-sheets too.

Fair, but I would not really call a single helix a 'fold', either!

Ok, so I'm playing with definitions here a bit. Clearly 2k9b adopts a helical structure so it is 'folded' in some sense. However it has no tertiary structure.

Structural proteins like collagen are different again. They have a simple fold that could be described as quaternary (multichain), although that is again an abuse of terminology.

There are also some small proteins (peptides?) held together by disulphide links that have no secondary strucure to speak of. I think these are Class 4 in CATH, but I do not remember.

What is an example of a beta-sheet peptide? Amyloid is beta, I thought, but sheets are not normally stable outside sandwiches, barrels, etc

> What is an example of a beta-sheet peptide?

WW domains[1] fold stably into a three-stranded sheet. Also, not strictly a sheet, but beta hairpin motifs (e.g. tryptophan zippers[2]) are known to be stable isolated from their parental domains.

[1]: http://www.rcsb.org/structure/5VTJ

[2]: http://www.rcsb.org/structure/1LE0

From the article:

> OTHER SHORT AMINO ACID chains, often called peptides or polypeptides, abound in cells, but they are pared-down remnants of bigger predecessors. Myoregulin and its diminutive brethren, in contrast, are born small.

Thats a bit confusing, as proteins _are_ polypeptides. All proteins are (poly)peptides, but not all peptides are proteins.

Reply on news.ycombinator.com