Here are some basic keyboard shortcuts:
- Move the cursor to the beginning of the word: Ctrl + Left .
- Move Caret to Line Start: Home
- Remove from Caret in Word Start: Ctrl + Backspace
- Remove from Caret to Line Start: Shift + Home , Delete
I assume that you want to Remove from Caret to Line Start ("backspace to begin of line").
If you want to perform this action with a single key, just write down the macro and assign it a key combination.
- Menu → Macros → Start Macro
- Press Shift + Home
- Click Delete
- Menu → Macros → Stop Macro
- Assign a name, such as "Delete to beginning of line"
- Assign a shortcut to your macro: Menu → File → Settings → Keyboard Key
Here is a screenshot of the settings dialog. I tested it and it works great. 
source share